Other forms: surprised; surprising; surprises
A surprise can be an unexpected or astonishing event, such as an ambush or a really great grade on a test you didn't study for.
Surprise can be a verb meaning to astonish or startle someone, a noun for the unexpected thing, or for the feeling produced by that surprise. It comes from the Latin word for "seize," and originally meant an unexpected military attack. When the novelist Charles Lever wrote in 1841 of "three cavalry regiments, their noiseless gestures and perfect stillness bespeaking at once that they were intended for a surprise party," he meant a surprise attack, not a birthday party.