所定
しょてい · shotei · JLPT N1 · na-adj
prescribed
📌 所 (that which) + 定 (fix, decide) = that which is fixed or prescribed
定 means fixed or decided, as in 定規 (ruler, a fixed measure). 所定 pairs it with 所 to mean the set or prescribed amount, time, or rule.
所 — door 戶 (left) + axe 斤 (right)
Originally a sound: an axe (斤) chopping wood near a door (戶), with 戶 also hinting at the pronunciation. Over time it was borrowed to mean 'place' or 'location,' and later became a grammatical particle nominalizing verbs ('that which…'). The concrete 'chopping' sense faded entirely.
定 — roof 宀 + 正 (correct/upright, phonetic)
Originally written with 宀 (roof) over 正 (upright/correct), suggesting a household settled and orderly under its roof. Over time 正 simplified to 㐬-like form at the bottom, and the meaning shifted from 'settled home' to the broader senses of 'fix, stable, decide.'