His companions always pay him a compliment on his piano playing.

pay 在这里的意思是"给予、付出"，指做出某种表达或行为。 him 是代词 he 的宾格形式，指代"他"。 a 是不定冠词，表示"一个"或"一次"。 compliment 是名词，意思是"赞美、称赞"。 pay him a compliment 是一个固定搭配，意思是"给予他赞美"或"称赞他"。