yawn

an involuntary intake of breath through a wide open mouth; usually triggered by fatigue or boredom; "he could not suppress a yawn"; "the yawning in the audience told him it was time to stop"; "he apologized for his oscitancy"

utter a yawn, as from lack of oxygen or when one is tired; "The child yawned during the long performance"

be wide open; "the deep gaping canyon"