- OE] By comes from a prehistoric Germanic *bi, which appears ultimately to be the same form as the second syllable of Latin ambi- (as in ambidextrous), Greek amphí (as in amphitheatre), and Old English ymbe, all of which meant ‘on both sides, round’. The original meaning of by thus seems to be ‘close to, near’. By is the basis of the prefix be-, as in befall and belong.
The Hutchinson dictionary of word origins. 2013.