- semiformal, semi-formal, black-tie - moderately formal; requiring a dinner jacket; "he wore semiformal attire"; "a black-tie dinner"
Antonym: informal (indirect, via formal)
- dinner jacket, tux, tuxedo, black tie - semiformal evening dress for men
--1 is a kind of formalwear, eveningwear, evening dress, evening clothes
- black tie - a black bow tie worn with a dinner jacket
--2 is a kind of bow tie