Self-radical and self-pictograph; Kangxi radical #76. The oracle bone and bronze forms drew a kneeling person leaning back with mouth wide open, breath visibly streaming out. From that yawn-image came the senses of releasing breath, wanting (lacking), and falling short (owing). Anchors a family of mouth-open verbs:
欢 (glad),
歌 (sing),
歇 (rest),
歉 (apologize).