- I know: that "bass" can mean "low in tone", "a string instrument with lower sound than a guitar", "a type of fish"
- I don't know: how any of those are pronounced. Like "ass"? Like "ace"?

@adriano

low in tone - like "ace"

a string instrument with lower sound than a guitar - same thing, because it's named as such because it's low in tone

a type of fish - like "ass"

@adriano I was sure about the former but had to doublecheck the latter https://en.wikipedia.org/wiki/Bass_(fish)

IPA to the rescue: /bæs/

Bass (fish) - Wikipedia