Happening or arising without apparent external cause:
— Spontaneous laughter.
— Spontaneous combustion.
— A spontaneous abortion.

synonym: self-generated.

Roget 748: free, free as air; out of harness, independent, at large, loose, scot-free; left alone, left to oneself.    in full swing; uncaught, unconstrained, unbuttoned, unconfined, unrestrained, unchecked, unprevented^†, unhindered, unobstructed, unbound, uncontrolled, untrammeled.    unsubject^†, ungoverned, unenslaved^†, unenthralled^†, unchained, unshackled, unfettered, unreined^†, unbridled, uncurbed, unmuzzled.    unrestricted, unlimited, unmitigated, unconditional; absolute; discretionary etc. (optional) 600.    unassailed, unforced, uncompelled.    unbiassed^†, spontaneous.    free and easy; at ease, at one's ease; degage [Fr.], quite at home; wanton, rampant, irrepressible, unvanquished^†.    exempt; freed etc. 750; freeborn; autonomous, freehold, allodial^†; gratis etc. 815; eleutherian^†.    unclaimed, going a begging.    ... show more

Roget 674: unprepared etc. (prepare); &c.; 673; without preparation etc. 673; incomplete etc. 53; rudimental, embryonic, abortive; immature, unripe, kachcha^†, raw, green, crude; coarse; rough cast, rough hewn; in the rough; unhewn^†, unformed, unfashioned^†, unwrought, unlabored^†, unblown, uncooked, unboiled, unconcocted, unpolished.    unhatched, unfledged, unnurtured^†, unlicked^†, untaught, uneducated, uncultivated, untrained, untutored, undrilled, unexercised; deckle-edged^†; precocious, premature; undigested, indigested^†; unmellowed^†, unseasoned, unleavened.    unrehearsed, unscripted, extemporaneous, improvised, spontaneous, ad lib, ad libitem [Lat.].    fallow; unsown, untilled; natural, in a state of nature; undressed; in dishabille, en deshabille [Fr.].    unqualified, disqualified; unfitted; ill-digested; unbegun, unready, unarranged^†, unorganized, unfurnished, unprovided, unequipped, untrimmed; out of gear, out of order; dismantled etc. v.. shiftless, improvident, unthrifty, thriftless, thoughtless, unguarded; happy-go-lucky; caught napping etc. (inexpectant) 508^†; unpremeditated etc. 612.    ... show more

Roget 612: extemporaneous, impulsive, indeliberate^†; snap; improvised, improvisate^†, improvisatory^†; unpremeditated, unmeditated; improvise; unprompted, unguided; natural, unguarded; spontaneous etc. (voluntary) 600; instinctive etc. 601.    ... show more

Roget 602: willing, minded, fain, disposed, inclined, favorable; favorably-minded, favorably inclined, favorably disposed; nothing loth; in the vein, in the mood, in the humor, in the mind.    ready, forward, earnest, eager; bent upon etc. (desirous) 865; predisposed, propense^†.    docile; persuadable, persuasible; suasible^†, easily persuaded, facile, easy-going; tractable etc. (pliant) 324; genial, gracious, cordial, cheering, hearty; content etc. (assenting) 488.    voluntary, gratuitous, spontaneous; unasked etc. (ask) etc. 765; unforced etc. (free) 748.    ... show more

Roget 600: voluntary, volitional, willful; free etc. 748; optional; discretional, discretionary; volitient^†, volitive^†.    minded etc. (willing) 602; prepense etc. (predetermined) 611^†; intended etc. 620; autocratic; unbidden etc. (bid) etc. 741; spontaneous; original etc. (casual) 153; unconstrained.    ... show more

Polish: samoczynny

Said or done without having been planned or written in advance.

synonyms: ad-lib, unwritten.

Polish: spontaniczny