formal

a lavish dance requiring formal attire

a gown for evening wear

being in accord with established forms and conventions and requirements (as e.g. of formal dress); "pay one's formal respects"; "formal dress"; "a formal ball"; "the requirement was only formal and often ignored"; "a formal education"

characteristic of or befitting a person in authority; "formal duties"; "an official banquet"

(of spoken and written language) adhering to traditional standards of correctness and without casual, contracted, and colloquial forms; "the paper was written in formal English"

represented in simplified or symbolic form

logically deductive; "formal proof"

refined or imposing in manner or appearance; befitting a royal court; "a courtly gentleman"