- by O.E. be (unstressed) or bi (stressed) "near, in, by, during, about," from P.Gmc. *bi "around, about" (Cf. O.S., O.Fris. bi, be "by near," Du. bij, Ger. bei "by, at, near," Goth. bi "about"), from *umbi (cognate with second element in PIE *ambhi "around," Cf. Skt. abhi "toward, to," Gk. amphi- "around, about"). Originally an adverbial particle of place, in which sense it is retained in place names (Whitby, Grimsby, etc.). Elliptical use for "secondary course" (opposed to main) was in O.E. This also is the sense of the second by in the phrase by the by (1610s). Phrase by and by (early 14c.) originally meant "one by one," modern sense is from 1520s. By and large (1660s) originally was nautical, "sailing to the wind and off it," hence "in one direction then another."
Etymology dictionary. 2014.