"Uh-huh"

YEP

Think of a casual three-letter reply that starts with the last letter of the alphabet.

"Uh-huh" is a casual way to say "yes," and "yep" is another informal version of the same thing. The clue is straightforward—no wordplay or tricks—just matching a common verbal nod with its three-letter equivalent. Think of it like how someone might respond in a quick, offhand way during a conversation.