The word 牙刷 (yáshuā, "toothbrush") is a straightforward compound noun formed by combining two characters: 牙 (yá), meaning "tooth", and 刷 (shuā), meaning "brush". It follows a common grammatical structure in Chinese known as a modifier-head compound, where the first character 牙 ("tooth") modifies and specifies the type of the second character 刷 ("brush"). This creates a clear and logical meaning, an instrument for brushing teeth, demonstrating how Chinese efficiently builds precise vocabulary by combining basic semantic units.