仮定
かてい · katei · JLPT N3 · noun
premise
🤔 仮 temporary + 定 settled = something settled for now: an assumption
仮 (kari) means temporary or provisional, as in 仮名 kana, the 'borrowed names' for sounds. 定 means to fix or decide. A hypothesis is a point you treat as settled for now, until the evidence decides it.
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.'