咬定 (yǎo dìng) is a vivid, idiomatic verb meaning 'to insist stubbornly' or 'to hold fast to a position without wavering.' Literally, 咬 (yǎo) means 'to bite,' and 定 (dìng) means 'to fix, settle, or determine.' Together, they evoke the image of clamping down with teeth—suggesting unyielding grip, tenacity, and refusal to let go of an opinion, claim, or stance. This phrase often carries a slightly negative or critical connotation, implying inflexibility or even doggedness in the face of contradictory evidence.

It commonly appears in contexts involving argument, accusation, or defense—especially when someone repeats a claim despite doubt or opposition. The phrase is frequently used in news reports, political commentary, and everyday disputes. While it can describe firm conviction, it more often highlights unreasonable persistence, especially when paired with words like '一口' (yī kǒu, 'in one breath') or '死' (sǐ, 'dead'). It’s a fixed two-character compound and functions as a transitive verb, typically followed by a clause or noun phrase indicating what is being insisted upon.