龃龉 is a formal, literary noun meaning 'disagreement' or 'discord', particularly between people's opinions or interests. It is most commonly used in written Chinese or formal speech, often in the set phrase 龃龉不合 (irreconcilable differences) or followed by a verb like 产生 (to arise). Learners should not use it in casual conversation; use 吵架 or 意见不合 instead.