involuntarily open one's mouth wide and inhale deeply, typically on account of tiredness or boredom

he began yawning and looking at his watch

(of an opening or space) be very large and wide

she started inching back from the abyss that yawned before her

the whole empty day yawned before me

a reflex act of opening one's mouth wide and inhaling deeply, typically on account of tiredness or boredom

he stretches and stifles a yawn