The word 巴掌 is a compound noun formed by combining two characters, 巴 and 掌, both of which independently relate to the hand. 巴 can historically refer to the palm or something broad and flat, while 掌 directly means "palm" or "sole". When combined, they create a reinforced, vivid term that specifically denotes the flat of the hand, most commonly used to mean a slap or palm strike. The formation is semantic, where the two synonymous or related morphemes unite to emphasize the concept of the entire hand used for striking, and it frequently appears in figurative expressions like "一个巴掌拍不响" (one hand alone can't clap), meaning a dispute requires two parties.