IPA: /spɒnˈteɪniəsnəs/
KK: /spɑnˈteɪniəsnəs/
The quality or state of acting on impulse or without premeditation; the ability to do things naturally and without planning.
Her spontaneousness made every outing an exciting adventure.
Spontaneousness → It is formed from "spontaneus" (from Latin *spontaneus*, meaning of one's own accord) and the suffix "-ness" (meaning the state or quality of). The word "spontaneousness" refers to the quality of being done or occurring naturally, without premeditation.
Think of actions that happen 'of one's own accord' — that's what spontaneousness means, reflecting the natural quality of being spontaneous.