0 in a way that is natural, often sudden, and not planned or forced: --
This story may prompt you to burst spontaneously into uncontrollable sobs.
Stem cells grown in petri dishes spontaneously try out new fates.
About 90% of patients with acute low back problems recover spontaneously within a month.
Nerve gases quickly affect the central nervous system. A person can't breathe, their eyes start blinking and their muscles move spontaneously.
Hundreds of people could spontaneously appear at my house for a party.
My best friend, who doesn't have kids, always expects me to do things spontaneously with her.
They gave him a mike, and he spontaneously interviewed everyone.