There is no remedy to knowing "monkey" has the "cut" vowel and "donkey" has the "lot" vowel except looking them up, and looking up more words, and yet more words after that.
Wait, what?
*looks it up*
Curse you, English!
Indeed.
In general, when it comes to English pronunciation, you should be careful of any stressed <on ov> sequence. This is because in the Latin script of the late Middle Ages, the sequence <un>
was indistinguishable from <nn uu nu>, so in late Middle English writers preferred to replace <un> with <on> at least in words that didn't come from Latin (like "monkey"). Regarding <ov>, the letter <v> didn't exist in the middle of a word at the time (it was a mere variant of <u> in word-initial position, as in <vnity> = unity), and as "uv" was actually <uu> and easily confusable with <un nn nu>, it was replaced by <ou> as well (now evolved to <ov>).
So this is the reason why "monkey, money, honey, none, done, one, come, won, son, London, month, Monday, wonder, wonderful, to love, to shove, shovel, dove (the bird, not the North American past tense of "dive"), glove, to hover, to covet, coven, cover, (un,dis,re)cover, oven, slovenly" have <o> even though they
all have the "uh" /ʌ/ vowel.
Contrast these with the likes of "phone, baloney, she drove, North American English he dove (British/Australian he dived), over, woven, supernova, Moldova, macaroni, bonus", which do have /oʊ/.
By analogy with "done", this was extended to "doth" /dʌθ/. Pretty recently, also colloquial "gonna" /ɡənə/ (/ˈgʌnə/ when rarely stressed), but beware "wanna" and "gotta" are /ˈwɑnə ˈgɑɾə/, southern England /ˈwɒnə ˈgɒtə/, the latter often [gɒʔə].
While we're at it, I would like to add that in general you should be
especially careful about a stressed <o> in what
looks like an open syllable (if only in spelling), whether in the second-to-last or third-to-last syllable, as in "s
ofa, pr
ofit" /ˈsoʊfə ˈpɹɑfɪt/ or "bi
ology"). In second-to-last open syllables, stressed written <o> is simply the most treacherous of all vowels, and in third-to-last syllables it's treacherous
in relation to other words of the same stem.
Compare "phot
o" /ˈfoʊtoʊ/ with /oʊ/ and phot
ography with /ɑ/ (southern England /ɒ/). The "photography" /ɑ/ is due to the general pattern of words stressed on the third-to-last syllable, as there was a shortening in Middle English that made any long vowels there become short, which means they usually have a descendant "traditional short vowel" today. Compare the suffix -ology [ˈɑlədʒi] and words like "curi
osity, aut
onomy, medi
ocrity" and "fid
elity /ɛ/, S
icily /ɪ/, norm
ality /æ/". This is why "nature" has /eɪ/ but "n
atural" has /æ/ (the latter was [ˈnæ-tʰju-ɹəl] in late Middle English, now /ˈnætʃɹəl/). Photography is a recent late 19th-century word, but the pattern still applies. Exceptions that occasionally pop up like "am
enities" /əˈminɪtiz/ (S. England /i:/) usually get corrected over time, so "am
enities" now usually has /ɛ/.
Just take the above as random advice from a war veteran to another war veteran.
Yeah, I remember the time when I realized how treacherous English orthography is and started looking every single word up in the dictionary, whether I know it or not. If I saw a word and didn't have a firm memory of ever looking it up before I would look it up. All those infinitude of familiar words pronunciation of which I've assumed over the years (and assumed wrong, as it turned out)...
Yet it still holds a few more surprises up its sleeve. And it's usually the simplest and most innocent looking words that trip you up.
You can imagine how traumatized I was when, after more than a decade studying English, I learned that "of" is actually pronounced /əv/, with a /v/ spelled <f>. I could not believe my eyes when I saw that in a dictionary.
I guess I could blame my English teachers and the EFL "communicative" culture at large for having never taught me a single thing about English pronunciation. Not like the teachers knew much anyway, whether they were native or not. I remember when, four or five years into studying English in El Salvador, I noticed I couldn't make sense of the vowel of "the", and I asked a teacher if the sound was "like (Spanish) A or like (Spanish) E", and then the teacher gave me a non-sensical answer. "It's a sound that doesn't exist in Spanish" would have been good enough. To think of all the pain that caused me years later...
This is why I also say non-native learners should insist that mis-pronouncing words should be basically acceptable, at least until English speakers get to fix their truly cursed writing system. Half-assedly retaining ambiguous late medieval spellings while expecting learners to pronounce everything correctly is a ridiculous thing to do, but here we are.