定規
じょうぎ · jougi · JLPT N2 · noun
rule
📏 Compound: 定 (fixed, set) + 規 (rule, standard) = a fixed standard for measuring
定 means fixed or settle, and 規 means rule or standard. A 定規 is the fixed straight standard you use to draw lines and measure length.
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.'