欠席
けっせき · kesseki · JLPT N3 · noun
absence
🪑 欠席 = lack + seat: your seat is missing you, so you're absent
欠 means lack or be missing, as in 欠点 (flaw). 席 means seat, as in 座席. Put together, a missing person in a seat means non-attendance. The opposite is 出席 (shusseki, attendance): go out to your seat.
欠 — person 人 below + open mouth 欠 top (yawning figure)
Pictograph of a person kneeling with mouth wide open, exhaling — originally depicting a yawn or breath. From this came meanings like 'to lack' or 'to owe', as if something is missing or breathed out. It now serves as a radical in characters related to breathing, singing, or desire (歌, 歡, 欲).
席 — 广 (shelter) + 巾 (cloth), over woven mat 苫
Originally a pictograph of a woven mat or rush mat used for sitting on the floor, with 巾 (cloth) hinting at the woven material under a shelter 广. Because guests were seated on such mats, 席 extended to mean 'seat,' 'place at a banquet,' and later any 'seat' or 'membership' in a group.