You've got one big hole in your back teeth.
Those strawberries were one hundred yen each, but they flew off the shelves.
Viet likes cream puffs so much that he eats at least one every single day.
The counter 個, which means individual on its own, refers to "an individual thing." This is usually a small thing, so it's used to count small things. This word here talks about one individual. A better way to translate that would be to call it one small thing.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. The いち gets shortened, but I bet you knew that already.