etymology of "sesquicentennial"

The word sesquicentennial means "150th anniversary". When I first found this out, I thought about the prefix sesqui- and what it could mean.

My first thought was that it meant 6/4 = 1.5, because it seemed that the syllables matched up with "six" and "quart". After deciding that that must be right, I decided to check online. To my surprise, it appears that the prefix literally means "half and".

Was my first revelation a complete coincidence or is there actually a legitimate reason for what I noticed?

Solution 1:

Well, according to Lewis and Short's "A Latin Dictionary", the derivation is actually:

sesquĭ (sesque ),
I. num. adv. [perh. contr. from semis-qui], one half more, more by a half. As a separate word it occurs only once: “ut necesse sit partem pedis aut aequalem alteri parti aut altero tanto aut sesqui esse majorem,” Cic. Or. 56, 188. But freq. joined in one word with designations of number or quantity, with the signif. of once and a half. Joined with numerals (octavus and tertius), like the Gr. ἐπί (in ἐπόγδοος, ἐπίτριτος, etc.), it denotes an integer and such a fraction over as the numeral designates; v. sesquioctavus, etc.

so I'd be inclined to think "coincidence". From such things are folk etymologies made.

Solution 2:

Actually, sesqui- is a contraction of semis and que

According to etymonline:

"pertaining to a century and a half," 1880, from L. sesqui- "one and a half" (from semis "a half" + -que "and") + centennial (q.v.). First recorded ref. is to Baltimore's. sesquipedalian

Also dictionary.com

[from Latin, contraction of semi- + as as ² + -que and]

So, there aren't related, and I would say it is just coincidence.