The word "燕尾服" is formed by sequentially combining three characters: 燕 (yàn), meaning "swallow" (the bird), 尾 (wěi), meaning "tail", and 服 (fú), meaning "clothing". This creates a literal compound meaning "swallow-tail garment", which directly refers to a tailcoat due to the visual resemblance of its split back to the forked tail of a swallow.