The lower lip of a person or animal.
- ‘She stopped working for a moment and stared at her, biting her underlip, twisting her mouth.’
- ‘It did not appear that such an inquiry had been tactful of her, the waitress noticed, nervously biting her underlip.’
- ‘Miguel would bite down on one side of his underlip, and slowly release it.’
- ‘He is pimply, his neck is thin, his blue eyes goggle, and his underlip extrudes.’
- ‘If the urgency of time wasn't dire enough, Cao bit his underlip, realizing had just earned himself a new enemy - politics.’