noun Also by.
Origin of bye1
Word Origin for bye
in sporting use, a variant of by (prep). Originally in cricket, "a run scored on a ball that is missed by the wicket-keeper" (1746); later, in other sports, "position of one who is left without a competitor when the rest have drawn pairs" (1883), originally in lawn-tennis.
shortened form of good-bye. Reduplication bye-bye is recorded from 1709, though as a sound used to lull a child to sleep it is attested from 1630s.
by the bye
Also, by the by. Incidentally, in passing, as in By the bye, my wife is coming too, or Exactly where do you live, by the by? The bye or second by in this term originally meant “a side path,” whence the current sense of “off the track” or “of secondary importance.” [Early 1500s] Also see by the way.