嘴唇 (zuǐchún) literally combines 嘴 (zuǐ), meaning 'mouth', and 唇 (chún), meaning 'lip'. Together, they refer to the fleshy, movable tissue that forms the border of the mouth — commonly used in everyday speech to mean 'lip' (singular or plural). While 唇 alone is more formal or literary (e.g., in medical or poetic contexts), 嘴唇 is the natural, colloquial term used in daily conversation, health discussions, and descriptions of appearance or sensation.

This word is often used when talking about physical conditions (e.g., dry or chapped lips), cosmetics (e.g., lipstick), expressions (e.g., biting one’s lips), or sensory experiences (e.g., tasting something with your lips). It functions as a singular noun grammatically — even though it refers to two lips, Chinese doesn’t pluralize body-part nouns like English does. You’ll hear it in phrases like 涂口红 on the 嘴唇 or feeling 嘴唇发麻 (numb lips).