INFORMAL Synonyms: 85 Similar and Opposite Words - Merriam-Webster
https://www.merriam-webster.com/thesaurus/informal
WEBSynonyms for INFORMAL: unconventional, unofficial, unorthodox, irregular, casual, unceremonious, heterodox, unauthorized; Antonyms of INFORMAL: formal, regular, conventional, routine, ceremonial, orthodox, proper, correct
DA: 1 PA: 84 MOZ Rank: 63