磨合
mó hé · HSK 7
to break in
⚙️ 磨 grind + 合 fit together = grind parts until they mesh = break in
磨 — stone 石 + hemp 麻 (phonetic)
A semantic-phonetic compound: 石 'stone' gives the meaning (grinding involves stones), while 麻 'hemp' supplies the sound. Originally referred to a millstone or the act of grinding grain, later extending to 'rub, polish, wear down' and figuratively 'to torment' or 'waste time'.
合 — 乛 (lid/roof) + 口 (mouth)
Originally a pictograph of a lidded vessel — a cover (亼) closing over an opening (口) — giving the core sense of 'come together, join, fit.' From 'fit/match' it extended to 'combine, unite, agree' and to measure-word uses. The reading hé reflects this 'joining' meaning.