A bass sound or instrument is the deepest. If a barbershop quartet sings “Happy Birthday” to you, the guy with the lowest voice is singing the bass part. A bass is also a type of saltwater fish.
The word bass has two main meanings with separate pronunciations — bass with a high vowel sound (like base) ironically refers to very low sounds — bass instruments and singers are in the lowest part of the musical range, like the low rumble of a bass guitar. If you say bass with a low vowel sound, it's a type of fish. That kind of bass doesn’t add much to a harmony but is delicious with mashed potatoes.