A yawn; the act or sound of opening the mouth wide from tiredness or boredom.
授業中に隣の席の生徒が大きなあくびをした。
The student next to me let out a big yawn during class.
疲れていて、朝からずっと欠伸が止まらない。
I'm tired and have been yawning constantly since morning.
赤ちゃんが欠伸をして眠そうだ。
The baby yawns and looks sleepy.
The kanji radical/name usage (radical 76 — 欠). A technical term used in kanji classification.
この字は欠伸（欠）の部首に属する。
This character belongs to the '欠' radical.