The word 衬衫 is formed through semantic combination, where two meaningful characters, each contributing a key aspect of the final concept, are joined. The first character, 衬 (chèn), carries the core idea of an "inner layer" or "lining", suggesting something worn against the skin. The second character, 衫 (shān), is a general term for a single-layer upper garment. When combined, they specify a particular type of garment: an "inner-layer upper garment", which is the direct and logical description for a shirt.