割合
わりあい · wariai · JLPT N4 · noun
rate
🍰 割合 = split (割) + fit together (合): how the split parts compare
割 (wari) means to divide or cut; it also names the old unit for one tenth, as in 3割 = 30%. 合 (ai) means to match or fit. Divide a whole, then match the parts against each other: that comparison is the ratio.
割 — 害 (harm, phonetic) + 刂 (knife radical)
A semantic-phonetic compound: the knife radical 刂 gives the meaning 'cut,' while 害 supplies the sound. The original sense was to cut or slice with a blade, which extended to 'divide' and 'allot a share.' Modern uses like 割爱 (give up something dear) preserve this idea of cutting away.
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.