noun
evening dress; formal evening wear
Refers to formal attire worn for evening social events such as dinners, parties, or galas.
彼女は夜会服を着てパーティーに出席した。
She attended the party wearing an evening dress.
礼服 is a general term for formal wear, including morning coats and tuxedos, not limited to evening events.
Compound of 夜会 (evening party) and 服 (clothing). The exact historical derivation is uncertain, but the term is conventionally associated with Western-style formal evening attire.