boo

An exclamation used to startle or playfully surprise someone.

"Boo! I got you!"

To shout 'boo' to express strong disapproval, especially at a performer.

"The crowd began to boo the unpopular politician."

A sound made to express disapproval, often by an audience or crowd.

"There were loud boos from the audience."

An exclamation used to express strong disapproval or contempt.

"Boo! That's a terrible idea!"