Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
betwixt, betwixt and between
Betwixt is an archaic or obsolescent preposition, except in the idiom and cliché betwixt and between, which means “neither the one thing nor the other,” “halfway between,” “in the middle,” “on the fence”: She simply couldn’t make up her mind, and so she hesitated there, caught betwixt and between.
