一口咬定

一口咬定:

Literally means:

assert categorically accuse definitely

Actually means:

It means asserting categorically, emphasizing the definiteness of one's statement. It is usually used to defend oneself or accuse others.

说得非常肯定。强调所说的确定无疑。多用于为自己分辩，或指证别人做了坏事。