freak out verb 4noun 1forms 5 verb4 •(informal) To react with extreme anger or fear, to the extent that one loses one's composure or behaves irrationally.When Peter saw the nail poking up through his foot, he freaked out and started hyperventilating. •(informal) To scare or unnerve someone.Don't take off your shirt when working behind the counter. You'll freak the customers out. •(informal) To be upset or nervous; to be scared or unnerved. •(informal) To adopt an unconventional (especially countercultural) persona or appearance.Formed in the heart of the British Invasion in 1964 as the Nevadas, the Jacks decided to freak out and grow their hair long. — 1990 noun1 •(slang, old-fashioned) A negative or unpleasant experience with LSD or another psychedelic drug. formsfreaked out · freaking out · freaks out · freak outs · freak-outs