Antonyms of adj semi-formal

1 sense of semi-formal

Sense 1
semiformal, semi-formal, black-tie -- (moderately formal; requiring a dinner jacket; "he wore semiformal attire"; "a black-tie dinner")

INDIRECT (VIA formal) -> informal -- (not formal; "conservative people unaccustomed to informal dress"; "an informal free-and-easy manner"; "an informal gathering of friends")
                                                                         

Similarity of adj semi-formal

1 sense of semi-formal

Sense 1
semiformal, semi-formal, black-tie -- (moderately formal; requiring a dinner jacket; "he wore semiformal attire"; "a black-tie dinner")
       => formal (vs. informal) -- (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")