～席
～せき · ～seki · JLPT N2 · noun
seating
💺🪑 席 began as a woven sitting mat (巾 = cloth), so ～席 counts places to sit
Before chairs, people sat on mats, and 席 meant that mat. It now means seat, and ～席 counts seats or places: 三席 (sanseki) is three seats. Sound hook: seki sounds like sit-key, the key number of people who can sit.
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.