- (often repeated several times) The sound of a cat coughing up a hairball.
- Also used of similar noises, particularly one made to show disgust or disapproval.
(third-person singular simple present gacks, present participle gacking, simple past and past participle gacked)
- (intransitive) To make a 'gack' noise.
- To expectorate a hairball.
Apparently from the sound made; believed to have first appeared in comic strips.