倍
ばい · bai · JLPT N4 · noun
double
倍 = person 亻 + 咅 (split apart): one split into two, so double
Sound hook: bai sounds like buy, as in buy one, get one, so you end up with double. Used as a counter too: 二倍 (nibai) is two times, 三倍 (sanbai) is three times.
倍 — person radical 亻 + 咅 (phonetic)
倍 is a semantic-phonetic compound: the person radical 亻 hints at the meaning, while 咅 supplies the sound 'bèi'. The original sense was 'to turn one's back on' or 'double back', which shifted to today's core meaning of 'times' or 'fold' in multiplication (e.g. 三倍 = threefold).