Noun

(uncountable) The quality of being spontaneous.

* Elizabeth Browning

Romney Leigh, who lives by diagrams, / And crosses not the spontaneities / Of all his individual, personal life / With formal universals.

(countable) Spontaneous behaviour.

(biology) The tendency to undergo change, characteristic of both animal and vegetable organisms, and not restrained or checked by the environment.

(biology) The tendency to activity of muscular tissue, including the voluntary muscles, when in a state of healthful vigour and refreshment.

Noun

(-)

Lack of premeditation; spontaneity.

*{{quote-book, year=1911, author=Burton Egbert Stevenson, title=The Mystery Of The Boule Cabinet, chapter=, edition= citation

, passage=The man who can carry through a carefully premeditated scene with an air of complete unpremeditation has an immense advantage. "Mr. Lester," he began, "I understand that you are the administrator of the estate of the late Philip Vantine?" " }}

*{{quote-book, year=1912, author=Dorothy Canfield, title=The Squirrel-Cage, chapter=, edition= citation

, passage=With a gesture as automatic as drawing breath, he jerked out his watch and looked at it, apparently to make sure of catching his trolley, although his valedictory was poured out with such a passionate unpremeditation that the action must have been involuntary and unconscious. }}