betwixt (prep., adv.)

Old English betweox "between, in the space that separates, among, amidst, meanwhile," from bi- "by" (see by) + tweox "for two," from Proto-Germanic *twa "two" (from PIE root *dwo- "two") + *-isk "-ish." With unetymological -t that first appeared in Old English and became general after c. 1500. Compare amidst. Betwixen also was a variant in Old and Middle English.

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Definitions of betwixt from WordNet

betwixt (adv.)
in the interval;
Synonyms: between