spontaneous

/spɑnˈteɪniəs/

/spɒnˈteɪniəs/

Something spontaneous happens when you're least expecting it. Spontaneous things are natural or instinctive, and they happen without warning.

If you plan to go to a movie and then you go, that's not a spontaneous thing. Ditching the movie at the last minute to go to the park? That's spontaneous. Spontaneous things happen all of a sudden, on the spur of the moment, without being planned. Spontaneous can also refer to things that happen without outside influence. Your parents will be happy if you do your chores spontaneously instead of waiting till they nag you.

Definitions of spontaneous

1. adjective

   said or done without having been planned or written in advance
   synonyms: ad-lib, unwritten

   unscripted

   not furnished with or using a script
2. adjective

   happening or arising without apparent external cause
   “spontaneous laughter”

   “spontaneous combustion”

   synonyms: self-generated

   impulsive, unprompted

   proceeding from natural feeling or impulse without external stimulus

   intuitive

   spontaneously derived from or prompted by a natural tendency

   instinctive, natural

   unthinking; prompted by (or as if by) instinct

   antonyms:

   induced

   brought about or caused; not spontaneous

   elicited, evoked

   called forth from a latent or potential state by stimulation

   iatrogenic

   induced by a physician's words or therapy (used especially of a complication resulting from treatment)
3. adjective

   natural, relaxed, or easy in manner, said of a person