Why is the word "potent" pronounced differently when standing by itself, versus being in the compound word "omnipotent"?

There is no rule for this.

to say it Omni-Potent is not incorrect, its just not the way most people pronounce the word Omnipotent, hence it is “incorrect” (not really, just not standard)

Vowel reduction. Unstressed vowels in English are often reduced to a schwa.

In the word “Newfoundland”, for instance, most people follow the vowel reduction standard which @Demosthenes explains, and say “NEWfundlind” Hence, that is standard and “correct”

But I’ve known natives of Newfoundland who pronounce it “New FOUND land”

Just go with whatever is standard with the people you address. And most people DO use the vowel reduction rule that @Demosthenes described in pronouncing the world Omnipotent”

Strange, isn’t it? I wonder the same about US states Kansas and Arkansas.

What is Arkansas but part of Kansas with the OzARKs (Ozarks)

Maybe some French name (Aux-Arc Above the Circle)) named the Ozarks. But I think the ARK in Arkansas is related to Ozarks

The only difference in pronunciation is that the accent is on diffferent syllables with “ni” receiving the emphasis in omnipotent while “po” gets the juice in potent.

It’s a characteristic of English that many words (not all) shift the accented syllable when they gain a prefix or suffix. Most (not all) native speakers shift the accent routinely and probably don’t even think about it, but it must be a pain to learn.

Someone into linguistics could probably tell us if it’s true mainly for Latin-based words, where Latin had its own similar rule about accenting the penultimate syllable. Remember that for some time Latin was seen as the model language, and there were attempts to force English to follow the model, especially in grammar, which is how we ended up with some odd rules that never did quite fit our evolving English.

Prefixed words like potent – omnipotent (and variants):

vocal – equivocal
syllable – polysyllabic
locution – interlocutor

Similar suffixed words:

transit – transition
locate – location (vacate – vacation, stagnate – stagnation, etc.)
equal – equality (mobile – mobility, able – ability, etc.)
miracle – miraculous
reptile – reptilian
victor – victorious
analog – analogy

Others like to shift accents when they go from noun to verb. Typically the noun has the accent on the first syllable, the verb on the second, although in many instances the distinction is being lost.

record
rebel
detail
permit (the noun PERmit is fast disappearing, but I still say it)
perfume
defect

As for why there isn’t more consistency, well, there are lots of good answers to that, but, as the saying goes in tech, it’s not a bug, it’s a feature.

I find it difficult to pronounce omni followed by potent. The transition from the ee sound at the end of omni to the p at the beginning of potent is difficult. It is easier to slur the two together and place the stress on the second syllable. Ease of pronunciation may also explain how we say impotent.

So…^^ you find it hard to say “keep” and “sleep” and “free pizza”?

Although I probably deserve a most egregious defenestration for suggesting this, I suggest that I add some spice to this thread by summoning the persisting perplexing and constantly confounding, MORPHAIL!

Would you believe that I used to write episode titles for the Perry Mason series?

Weren’t those usually alliterative?

Exactimundo!

Sometimes it’s such a struggle to avoid alliteration. ;-)

”...persisting….”

*Persistently

Morphail is exactly who we need, @Brian1946, and that’s who I thought of when I mentioned “someone into linguistics.” Morphail has been absent for a while but is still missed.

The emphasis, or accent, shifts when you add more syllables. It’s why Spanish uses accent marks, and probably other languages too. In Spanish there are rules for if there are X amount of syllables in a word the the emphasis is on the 1st syllable or 2nd, etc. If the emphasis is on a different syllable than the rule, then in written Spanish they put an accent mark to let you know not to follow the standard rule. In English you just have to know how it’s pronounced, and half the country might pronounce it differently anyway. English is often messy.

@Jeruba , You make a good point. Perhaps it is the long o in potent that makes the pronunciation difficult. Just try saying omni-potent three times quickly.

@LostInParadise Are you sure about that?

I see your point loli. We have little to compete with you when it comes to tongue tying pronunciations. I swear I don’t understand how you folks manage a conversation without spitting all over one another.