Learn English – American English Pronunciation of “o” sound long or short

The argument over the US/UK pronunciation of “risotto” stems from how the first “o” is pronounced in Italian.

It is a sound we don't really make in English, lying almost exactly between our short and long “o” sounds. To the US ear, it sounds more like a long “o”; shorter in duration, but essentially the same vowel sound. To the UK ear, it sounds more like a short “o” rhyming with “pot”. For the US speaker the second syllable rhymes with the Italian word for eight, “otto” (oh-toh). For the UK speaker, who's long “o” sound is more flexed and drawn out, this would sound a bit strange (oe-toe)—and no doubt he‘s been told as much—so he rhymes it with "motto" or the name “Otto” to get a bit closer.

The same phenomenon arises around the pronunciation of the Spanish “Rioja”, with the US speaker saying “Ree-ò-ha” (approximating the Mexican Spanish pronunciation of the “j” as an “h”), and the UK speaker saying “Ree-ock-ka” (and doing something strange and interesting with that “j”, turning it into a “k” in an attempt to mimic an aspirated “kh” sound).

Its all a bit baroque (US: rhymes with “joke”; UK: rhymes with “rock”), the native pronunciation lying almost exactly in between the two.

Except for words imported from non-Latin/Germanic languages, words with ortography matching the following regular expression will have the matching part realized as /er/: *a[ei]r[iey]* provided that the matching syllable has the word-stress.

In the "Shorter Oxford English Dictionary" (BrE pronunciations) the expression matches over 450 headwords (including false positives where "a" is not in a stressed syllable) with only a couple exceptions, like "Bohairic" (via Arabian), "dairi" (via Japanese), "etaerio" (From Greek via French; exception to the non-Latin precondition). In the cases that I investigated Merriam-Webster's Collegiate was also providing the phoneme /e/ for the syllable that includes the letter "a".

It appears that if the consonant was not "r" then the realization would be most often /ei/ (as in "tale", "calix", "agave" (BrE), "baby","navy", "zamia") but the "r" reduces that to the less heavy /e/. The rise is likely related to the stressed syllable being open.

There exist other examples, with all requiring that the 'a' be in a stressed syllable but there appear to be more exceptions than matches in the cases that I investigated ("scarus", "marum", "larum", "garum", --> /e/ but most other matches are a false positive).

This observation mostly matches the first comment of Janus Bahs Jacquet but strengthens the conditions for the raise to happen. Will be glad to revise if someone is able to provide a condition that provides a higher accuracy.