Etymology of "bizarre"?

TLDR: Not Basque but Italian, but beyond that, we don’t know.

The OED reports Littré’s Basque (Euskera) theory, but does not quite seem to believe it (bold emphasis mine):

Etymology: mod.Eng. (17th c.), a. Fr. bizarre ‘odd, fantastic,’ formerly ‘brave, soldier-like’; cf. Sp. and Pg. bizarro ‘handsome, brave,’ Ital. bizzarro ‘angry, choleric,’ dial. Fr. (Berry) bigearrer to quarrel. Littré suggests that the Spanish word is an adaptation of Basque bizarra beard, in the same manner as hombre de bigote moustached man, is used in Sp. for a ‘man of spirit’; but the history of the sense has not been satisfactorily made out.

• 1667 Evelyn Mem. (1857) III. 161 We have hardly any words that do so fully express the French··naivete, ennui, bizarre, concert··emotion, defer, effort··let us therefore (as the Romans did the Greek) make as many of these do homage as are like to prove good citizens.

Of the Spanish, the RAE says only that it comes from the Italian bizzarro which it glosses as having meant anger-prone in that language. They do point out in their Diccionario panhispánico de dudas that the Spanish word only means “valiant”, not “strange” or “extravagant” like the French or English sense of the word, which it calls a “censurable semantic calque” in Spanish. However, the truth is that it is more and more getting used that way, which perhaps is why they complain. :)

Meanwhile, if you look in Littré, you find this:

ÉTYMOLOGIE

Berry, bigearre ; bigearrer, disputer ; espagn. et portug. bizarro, magnanime, vaillant ; ital. bizarro, emporté, colère. Notre mot français vient de l'espagnol et il a eu d'abord le sens de vaillant, brave (voy. à l'historique l'exemple de Lanoue). L'italien a, il est vrai, un substantif bizza, colère ; mais bizarro n'en peut dériver, puisque le suffixe arr n'est pas italien. Tout porte à croire que le mot est d'origine espagnole ; dès lors deux étymologies s'offrent : le basque bizarra, barbe, décomposé par Larramendi en biz arra (qu'il soit un homme) ; et l'arabe basharet, beauté, élégance, d'où vaillant, chevaleresque, puis les sens de colère, emporté, extravagant.

Which claims that the French word comes from Spanish, but that there are two competing theories, one from Basque and the other from Arabic. The Basque theory it traces to biz arra for subjunctive “[that one/he] be a man” in Basque. For the Arabic theory it tries to connect Arabic basharet related to elegance and thence to valiance and once again towards high-spirited.

An article on About World Languages just echoes the common bearded theory:

from French bizarre ‘odd, strange’, possibly from Basque bizar ‘beard’ (possibly due tof the strange impression made in France by bearded Spanish soldiers)

The most extensive treatment of the possible origin of the word comes from this Chilean site on hard-to-find etymologies, which says in part:

El origen del español bizarro lo ha estudiado Corominas en su Diccionario Crítico Etimológico Castellano e Hispánico (DCECH) en un artículo muy bien documentado con gran profusión de datos históricos y lingüísticos y que no deja lugar a dudas sobre su origen italiano: Viene del término bizzarro "iracundo", "furioso", "fogoso", que, a su vez, deriva de bizza "ira instantánea", "rabieta", término éste ya de origen incierto.

Loosely translated, that paragraph says that the origin of the Spanish word bizarro was studied by Corominas in his Diccionario Crítico Etimológico Castellano e Hispánico in a very well-documented article with a great profusion of historical and linguistic data, and that it leaves no room for doubt regarding the Italian origin. However, the Italian word bizza (meaning quick anger) which the Italian word bizzarro in turn derives from is itself of uncertain further origin.

I should point out that earlier in the French citation, Littré disregards the bizza theory on the grounds that -arro isn’t an Italian suffix.

They then continue with this, addressing the Basque myth:

El pretendido origen vasco lo analiza Corominas desde sus comienzos y le hace un seguimiento esclarecedor. Parece ser que el primero en sugerirlo fue Baltasar de Echaue, en su obra Discursos de la antigüedad de la lengua cántabra bascongada (1607), donde la hacía derivar de "viçarra, hombre de barba o pelo en pecho". Se aceptó esta etimología con rapidez y escaso sentido crítico, especialmente por autores de gustos marcadamente vascófilos, sin reparar en que el euskera bizarr significa únicamente "barba".

Tampoco se reparó, y esto parece menos excusable en los estudios diacrónicos de una lengua, en el hecho incontestable de que en italiano la palabra está en uso continuado desde, por lo menos, el s. XIII (1212), mientras que en español no aparece hasta el último tercio del s. XVI (1569). En vano se la busca en ningún autor medieval -salvo una aparición aislada: en la traducción precisamente de la Divina Comedia de Dante hecha por el Marqués de Villena en 1428, lo que habrá que interpretar mejor como una interferencia léxica del italiano-, ni tampoco en los lexicógrafos de los ss. XV y XVI como Alonso Fernández de Palencia (1490), Elio Antonio de Nebrija (1495), Pedro de Alcalá (1505), Cristóbal de las Casas (1570) o Alonso Sánchez de la Ballesta (1587).

The gist of that, and the rest of the article, is that they don’t buy the Basque origin theory one single bit.

The Basque origin theory was seized upon by Basque sympathizers even though the Basque word only means “beard” not “valiant”. There is also a distinct paucity of medieval evidence for the word in Spanish, appearing uniquely in a translation of Dante, where it was taken for a loanword. The rest of the article also casts doubt on whether the Italian word first appeared in French or in Spanish.

So although the strongest arguments deny an ultimately Basque origin for bizarre, no completely convincing alternate theories for the ultimate origin present themselves either.

That’s because although English bizarre comes from Italian bizzarro by way of French, we aren’t sure that the Italian bizzarro dating from 1212 actually comes from Italian bizza (“quick anger”) — plus even if it does, we don’t know where bizza comes from, for there the trail grows cold.

In Italian

In a comment Josh61 pointed out what the Italians think of their word bizzarro. Specifically, what Ottorino Pianigiani thought of it in his Vocabolario etimologico della lingua italiana of 1907, which I quote below (using the original spelling):

biżżarro

Sembra che il primo significato sia stato quello che tuttora remani'nello spanuolo e nel portoghese (bizarro) di Animoso, Baldo, Generoso, Liberale (onde probabilm. il nome propr. di Pizzarro) e che tragga dal basc. BIZARRA prode, valoroso, che si presterebbe anche a spiegare il senso di facile a infierire, stizzoso, iracondo, già antico nell’idioma italiano, p. es.

Lo fiorentino spirito bizzarro
in sè medesmo si volvea co’denti.
(Dante, Inf. VIII, 62);

nonché l’altro di vivo, brioso. Quello però che non sta in armonia cogli accennati significati è il senso oggi prevalente di Capriccioso, Stravagante, Fantastico, Strano, che domina nel francese (_^BIZARRE), e che l’Heise crede spiegare narrando come i francesi del mezzogiorno cosí appellassero gli spagnuoli, perché solit portare lunga barba, che in basco se dice _^BIZARRA, e siccome gli spagnuoli erano famosi per i loro modi ampollosi e strani cosí l’aggettivo _^BIZARRE a poco per volta sarebbe passato al significato di stravagante. Invece il Muratori propone il fr. _^BIGARREdi colore variegato da _^BIGARRERcat. _^BIGARRARscreziare (che il Menage trae del lat. _^BIS e _^VARIÀRE, altri da _^BIS e fr. _^CARRÉquadrato, quasi fatto a quadri) lo che sarebbe in certo modo avvalorato dall’applicazione frequente che se fa della voce _^BIZARRO alle stoffe di colori stavaganti, d’done poi sarebbe passata a designare il carattere stravagante di una persona. Ma forse, secondo che si applia a persona o a cosa, è voce distinta e di varia origine, quantunque suoni ugualmente. Altri inoltre partendo dal stizzoso, ha creduto trovare spiegazione in _^BIZZA con la terminazione germanica _^ÀRDO cambiato in _^ÀRRO, e si è pensato perfino al pers. _^BIZARsdegnarsi, che farebbe al bisogno se avvese anelli di congiunzione nelle lingue euopee. Il Caix finalmente con piú artificio lo vorebbe contratto da _^REBIDIÀRIO, formato de _^REBÍDIO usato in antico per aribrtrio (cfr. Ghiribizzo).

Deriv. Biżżarraménte; Biżżaría; Imbiżżarriri; Sbiżżarrsírsi.

The summary is that they aren’t sure either, but they think the existing Spanish and Portuguese sense of the word is the original Italian sense, too, despite the “extravagant” sense it has taken on in recent years, citing Dante having used it in this way.

They then recount the opinions of various scholars on various possible origins, ranging from the strange and bombastic ways of Spaniards to mottled colors of paintings leading to persons of eccentric character, and the even more whimsical theories.

They also suggest a possible connection with a Germanic word for being angry, and theorize that the Germanic -ardo suffix became -arro. Regarding bizza they say:

bíżża

La Crusca ritiene che sia forma varia ed intensiva di _^ÍZZA (v. q. voce), ma invece pare che possa trarsi assai bene dall’ a. a. ted. _^BIZZAN = mod. _^BEISSEN pungere e propr. mordere: onde ne verrebbe il significato di puntiglio (v. Biscia). — Collera, Stizza, nella quale per lo piú è del capriccioso, simile a quella di un cavallo punto da’ tafani, e dicesi piú specialmente dei bambini e delle donne che si adirano e strillano per cose da nulla.

Deriv. Biżżóso.

Which mentions the connection to Proto-Germanic bizzan, meaning to sting or bite, or pique. It seems to means capricious anger like a horse stung/bitten by a fly.

Pizza and Pizarro

One commenter thought that the current pronunciation of bizarre in French or English or bizarro in Spanish doesn’t sound anything like the Italian sound heard in pizza, and so disbelieves the proposed Italian origin. As Janus rightly points out in comments, there is no spelling conflict between the Italian and the Spanish versions, since when Spanish imported it, its z would have been /d͡z/ anyway, as this diagram from the referenced article shows:

One should probably also mention the surname of Francisco Pizarro, the Spanish conquistador of the Incan Empire, as well as the Spanish words pizzara, pizarrón meaning chalk and chalkboard. Although the surname might be a case of nominative determinism if it was equated with bizarro brave, apparently the chalky words’ origin is also debated. The RAE says only that pizarra is of inconclusive origin.

Inconclusive, but what are the theories? In the website Recursos Didácticos Docencia Universitaria they write:

Antiguamente trozos de pizarras (tipo de piedra) se usaban de forma individual y en dimensiones pequeñas, por lo que se ideo utilizar la pared pintada directamente o sobre madera en mayor dimensión, pero conservando su nombre de pizarra o pizarrón dado su nueva extensión.Los primeros datos sobre el empleo del pizarrón datan del siglo XVIII.

La palabra pizarrón proviene de “pizarra”, que es una roca de grano muy fino de color negro azulado que se puedes dividir fácilmente en hojas planas. Pizarra tiene su origen en el latín “fissus”, que significa hendido, abierto. Otros autores afirman que su origen es vasco de la palabra “pizarra”.

So here again we have a dispute about whether a very similar word derives from Basque or from another language, in this case Latin fissus, which I myself have trouble believing but stranger thing have happened.