Antonyms of adj ceremonious

1 of 2 senses of ceremonious

Sense 2
ceremonious, conventional -- (rigidly formal or bound by convention; "their ceremonious greetings did not seem heartfelt")

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 ceremonious

2 senses of ceremonious

Sense 1
pompous, ceremonious -- (characterized by pomp and ceremony and stately display)

Sense 2
ceremonious, conventional -- (rigidly formal or bound by convention; "their ceremonious greetings did not seem heartfelt")
       => 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")