formalwear(n = noun.artifact) evening clothes, evening dress, eveningwear - attire to wear on formal occasions in the evening;
is a kind of attire, dress, garb
has particulars: balldress, dinner dress, dinner gown, evening gown, formal, black tie, dinner jacket, tux, tuxedo, dress suit, full dress, tail coat, tailcoat, tails, white tie, white tie and tails

   attire to wear on formal occasions in the evening. [WordNet 1.5]