'White-tie' definitions:

Definition of 'white-tie'

(from WordNet)
adjective
Requiring white ties and tailcoats for men; "a white-tie occasion"

Definition of 'White-tie'

From: GCIDE
  • White-tie \White-tie\, a. requiring formal evening clothes, usually interpreted as a white bow tie and a tailcoat for men, and a formal evening dress for women; -- as, a white-tie reception at the embassy. Contrasting with black-tie and informal. [PJC]