1.Inf. I'm pretty sure that something is so or that something will happen. Bob: You're late. I bet you miss your plane. Rachel: No, I won't.Sue: I'll bet it rains today. Alice: No way! There's not a cloud in the sky.
2. Inf. I agree. (Often sarcastic.) Tom: They're probably going to raise taxes again next year. Henry: I bet.Fred: If we do that again, we'll really be in trouble. Andrew: I'll bet.