Longman Dictionary of Contemporary English
Wiktionary
a. spontaneous; impromptu.
WordNet
adj. in response to an unforeseen need; "a spur-of-the-moment party"
Usage examples of "spur-of-the-moment".
Lin worked with it, rendering the muscle tone in abstract streaks and drips, a spur-of-the-moment rescue.
It was just a spur-of-the-moment thing-we didn't have classes on Halloween and the weather was so nice and Miles said, hey, let's go out to Chimney Rock.
I finally found a small canned ham, and with this, some canned new potatoes, and three of the highly valuable eggs from our community's small flock of chickens, managed to make a sort of ham and potato salad, moistened with a spur-of-the-moment, homemade mayonnaise I whipped up from the yolk of one of the eggs and the corn oil we had in fair quantity.
It really wasn't fair that such a trivial, spur-of-the-moment, seemingly harmless decision such as taking an iced coffee to-go could change the entire course of a girl's life.