spontaneous
adj.adj. happening naturally or suddenly without being planned in advance. You use this to describe someone who acts on their feelings in the moment.
adj. occurring as a result of a sudden inner impulse or inclination and without premeditation or external stimulus. Often describes human behaviour or physical processes that happen without an obvious trigger.
We took a spontaneous trip to the beach today.
The crowd broke into spontaneous applause when the young musician finished her difficult solo.
While some researchers argue that the chemical reaction was spontaneous, others believe it was catalyzed by trace amounts of minerals present in the water supply.
Learned borrowing from Late Latin spontāneus.
Often follows a linking verb like 'be' or 'become'; can also modify nouns directly.