informal

1 not rigidly following established form, custom, or rules an informal meeting allowed everyone to get acquainted Synonyms heterodox, irregular, unceremonious, unconventional, unorthodox Related Words unauthorized, unofficial; casual, easygoing, familiar, free and easy, lax, loose, offhand, relaxed, ultracasual Near Antonyms correct, decorous, proper; constrained, inhibited, restrained, rigid, stiff, stuffy, uptight Antonyms ceremonial, ceremonious, conventional, formal, orthodox, regular, routine

2 not designed to be worn only on special occasions chose an informal flowery dress Synonyms everyday, casual, workadayRelated Words dégagé, relaxed, sporty; dressed down; shabby, sloppy, slovenly, unkemptNear Antonyms best, Sunday; dressed up; chic, elegant, fashionable, smart, stylish; neat, tidy, trim; semiformalAntonyms dressy, formal, noncasual

3 used in or suitable for speech and not formal writing the use of informal language in a scholarly article is really inappropriate Synonyms conversational, colloquial, nonformal, nonliterary, unbookish, unliterary, vernacular, vulgarRelated Words dialectal, dialectical (also dialectic), nonstandard, regional; incorrect, nongrammatical, substandard, uneducated, ungrammatical, unlearned; slang, slangyNear Antonyms standard, undialectical; correct, educated, genteel, grammatical, properAntonyms bookish, formal, learned, literary