informal

Synonyms: breezy colloquial congenial cool democratic down home easy easygoing everyday extempore familiar folksy frank free free-and-easy homey improv inconspicuous intimate laid back loose low-pressure mellow mixed motley natural off-the-cuff open ordinary relaxed spontaneous sporty straightforward throwaway unceremonious unconstrained unconventional unfussy unofficial unrestrained urbane without ceremony

Antonyms: buttoned-up ceremonious dressed-up formal official rigid stiff