double, twice, times, fold
倍 centers on multiplication: making something double, twice as much, or several times larger. The idea of 'fold' extends naturally from that same sense of repeated increase.
倍 combines 亻 (person) with 咅, which likely contributes the sound and carries a sense of doubling or increasing. The exact historical development of 咅 is uncertain.
A person 亻 standing beside 咅, which looks like a mouth 口 over a stand 立, as if someone is speaking twice as loud or repeating themselves: that doubling is the core of 倍.
For バイ, imagine buying one item and getting double: buy -> バイ, and the person 亻 gets twice as much.
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double; twice (as much)
magnification; leverage; amplification; scaling factor; scale factor
doubling; double
(much) more than others; exceedingly; extremely; unusually
multiple
double speed (data transfer, video playback, etc.); 2X speed
(harmonic) overtone; harmonic; harmonic partial
double amount
doubling (repeatedly); multiplying
doubling
hundredfold; hundred times as much
genome doubling
marker size scale factor
multiplying by one; original amount
monoploid; haploid (with a single set of unpaired chromosomes)
a single seed can eventually produce a great harvest; even the smallest beginning can generate a greatest profit; watch the pennies, and the pounds will look after themselves
three times (as much); treble; triple; threefold
triploid (organism, cell, etc.); triplont
win worth 24000 points (or, if dealer, 36000 points)
double; twice (as much); twofold