What is yawn?
yawn is (verb) to open your mouth wide and breathe in and out deeply when you are tired or bored He went on speaking for so long that half the people at the meeting started yawning or started to yawn. Noun 1. the act of opening the mouth when you are bored or going to sleep His yawns made everyone feel sleepy. to stifle a yawn to try to prevent yourself from yawning 2. some- thing which is very boring The concert was just one big yawn.
source: Easier English, Student Dictionary Upper Intermediate Level