Similar words that change from "-ter" to "tre"
Solution 1:
According to Wikipedia:
In British usage, some words of French, Latin, or Greek origin end with a consonant followed by -re, with the -re unstressed and pronounced /ər/. Most of these words have the ending -er in the United States. The difference is most common for words ending -bre or -tre: British spellings centre, goitre, kilometre, litre, lustre, mitre, nitre, reconnoitre, saltpetre, spectre, theatre, titre, calibre, fibre, sabre, and sombre all have -er in American spelling.
... Many words spelled with -re in Modern French are spelled with -er in both British and American usage; among these are chapter, December, diameter, perimeter, disaster, enter, filter, letter, member, minister, monster, October, November, number, oyster, parameter, powder, proper, September, sober, and tender.
The ending -cre, as in acre, lucre, massacre, mediocre, is preserved in American English, to indicate the c is pronounced /k/ rather than /s/.
After other consonants, there are not many -re endings ...: louvre and manoeuvre after -v; meagre (but not eager) and ogre after -g; and euchre, ochre, and sepulchre after -ch. In the United States, ogre and euchre are standard; manoeuvre and sepulchre are usually spelled as maneuver and sepulcher; ...
The e preceding the r is retained in American-derived forms of nouns and verbs, for example, fibers, reconnoitered, centering, ... fibres, reconnoitred and centring respectively in British usage. ...
Exceptions. ... include Germanic words like anger, mother, timber, water and Romance words like danger, quarter, river.
...
More recent French loanwords retain an -re spelling in American English. ... double-entendre, genre, or oeuvre. ... cadre, macabre, maître d', Notre Dame, piastre, and timbre.
Solution 2:
Imposing '-er' over '-re' on words from old French is one of the orthographic simplifications by Webster when he wrote his dictionary of American English. These alternate spellings are particular to the USA, and are otherwise not preferred.
Solution 3:
In English, final unstressed -re after a consonant is pronounced /ər/. Most of the words that are written with final -re in British English are written with final -er in American English to reflect the pronunciation. The list of such words, apart from lustre/luster, includes:
- calibre/caliber
- centre/center
- fibre/fiber
- goitre/goiter
- kilometre/kilometer
- litre/liter
- mitre/miter
- nitre/niter
- reconnoitre/reconnoiter
- sabre/saber
- saltpetre/saltpeter
- spectre/specter
- theatre/theater
- titre/titer
There are words that are written with the final -er in both American and British English, even when the original words from which the English words are derived end in re, or contained a consonant cluster like tr:
- diameter (from Old French diametre)
- disaster (from Italian disastro)
- filter (from Old French filtre)
- monster (from Old French monstre)
- number (from Old French numbre)
- oyster (from Old French oistre)
- perimeter (from Greek perimetros)
Reference: Wapedia.
Solution 4:
There are many words like these: centre, centimetre, fibre, calibre, litre, just to name a few. (Other answers have given good longer lists.) I’m sure there are some exceptions escaping me, but all or almost all of these have the same history:
Generally, the -re forms are older: these words came into English from French, where they were (and mostly, still are) spelled similarly (centre, centimétre), and where the pronunciation reflects the -re ending.
After entering English, the pronunciations became anglicised and no longer matched the spellings — so for proponents of spelling reform, these words were an obvious target. Most influentially, Noah Webster used the -er forms in his dictionary and his ‘Blue-backed Speller’; and (like many of his reforms), they caught on across the US, and are now the standard spellings there.
As far as I know, most other English-speaking countries use the -re forms; but as the influence of American English increases for ESL students, this may well now be changing.