衬衣(chèn yī) - shirt in Mandarin

衬衣 (chènyī) is a shirt, the button-up garment worn on its own or under a jacket. 衬 (chèn) carries the idea of lining or setting something off, and 衣 (yī) is the general word for clothing, so the compound points at the layer worn close to the body under something else.

You will also meet 衬衫 (chènshān) for the same garment; the two are near-synonyms and regional preference decides which one comes to mind first, with 衬衫 (chènshān) slightly more common in everyday speech and 衬衣 (chènyī) just as correct.

The measure word is 件 (jiàn): 一件衬衣 (yí jiàn chènyī), one shirt. In a formal setting it pairs naturally with 领带 (lǐngdài), tie, and 西装 (xīzhuāng), a suit.