surprise party

a party or celebration planned for someone as a surprise.

something that surprises someone.

Origin of surprise party

First recorded in 1835–45

Teacher nodded, though at that particular moment she had not the vaguest idea what the surprise-party was to be.

Dixie Martin |Grace May North
She took Frederick Edrington into her confidence, and a surprise-party was planned and carried out.

Dixie Martin |Grace May North
Not long ago I happened to be one of a number of fair ladies and brave men assembled at what is called a 'surprise-party.'

Continental Monthly, Vol. II. July, 1862. No. 1. |Various
A surprise-party of redstarts breaks into full play around him.

Fisherman's Luck |Henry van Dyke

"I mean that I am not used to a surprise-party and to playing with strangers," was the rude and angry answer.

A Flock of Girls and Boys |Nora Perry