An Etymological Dictionary of the German Language/zwischen
zwischen, adv. and afterwards prep., ‘between, among,’ from the equiv. MidHG. zwischen, zwüschen, adv. and prep. Orig. a shortened form of the adverb. expressions MidHG. inzwischen, under zwischen, OHG. in zwiskên, untar zwiskên, ‘between each pair.’ Allied to MidHG. zwisc, zwisch, adj., OHG. zwisk, zwiski, adj., ‘twofold, two and two’; comp. OSax. twisk, Du. tusschen, E. betwixt.—Derivatives ModHG. dazwischen, inzwischen.