约定
yuēdìng · HSK 6
agree upon
🤝 约 promise + 定 settled = nail down a promise
DING like a bell — once it dings, the deal is done. 约 is the verbal promise, 定 fixes it so no one can back out.
约 — silk radical 糹/纟 + ladle 勺
约 combines the silk radical 糹 with 勺 (ladle), which provides the sound. Originally it referred to binding or tying with silk cords, from which came the meanings 'to bind by agreement,' hence 'pact, appointment,' and later 'approximately' (a loose, tied-up estimate).
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.'