Synonyms of spontaneous

1 Syllable

free, gut, down

2 Syllables

reflex, upfront, improv, lamber, up-front, adlib, guter, knee-jerk, naive, chatty, simple, bandaid, chattier, unspoilt, will-less, casual, re-flex, band-aid, offhand, ad-lib

3 Syllables

unbidden, unstudied, ad-libbing, haphazard, informal, impetuous, unfussy, unwilled, gratuitous, unforced, unasked, adlibbed, unjaded, free-willed, hair-trigger, unplanned, unguarded, hot-and-cold, unprompted, childlike, impromptu, unconscious, instinctual, unartful, hang-loose, outgiving, unscripted, relaxed, natural, hairtrigger, throwaway, off-the-cuff

4 Syllables

improviso, undesigning, unprepared, instantaneous, unaffected, aleatory, automatic, low-pressure, free-and-easy, unrequested, unselfconscious, unassumed, unlabored, unprescribed, voluntary, unreflecting, instinctive, unself-conscious, unhampered, unrepressed, improvised, intuitional, uncompelled, uncontrived, impulsive, emotional, undemanded, extempore, reflexive, unconstrained, uncontrolled, intuitive, uncircumspect

5 Syllables

spur-of-the-moment, extemporaneous, unsolicited, autogenetic, unembarrassed, inevitable, matter-of-course, unmeditated, unintentional, uncalculated, involuntary, irresistible, unavoidable, second-nature, unpremediated, uninhibited, autoschediastic, extemporary

6 Syllables

unsophisticated, improvisatory