spontaneous

"You only have one youth, you have to try a spontaneous trip with your friends," one of four told local media.

Shapiro predicted the neighborhood, nicknamed “Poet’s Corner,” would erupt into a spontaneous street party if Harris wins.

That unpredictability has led people to compulsively check the stores’ Instagram Stories for news of spontaneous restocks.

That bleed was spontaneous, that as far as we're led to believe wasn't triggered by exercise or rugby, it was spontaneous, and that's what caused the swell up.

A tip is "an uncalled for and spontaneous payment offered by a customer,” according to the government, whereas a service charge is "an amount added to the customer’s bill before it is presented”.