测定
cè dìng · HSK 6
to survey and evaluate
📏 测 = measure + 定 = determine; together: measure and determine
测 carries the water radical 氵 and originally meant gauging depth; 定 means to fix or settle. Combined, 测定 is the act of measuring something and then settling on a value — survey plus evaluation.
测 — water radical 氵 + 则 (rule/standard)
测 combines the water radical 氵, hinting at meaning, with 则 (rule, standard), which also supplies the sound. Originally it referred to gauging the depth of water, then broadened to mean measuring, surveying, or testing in general.
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.'