Whilst
来自Big Physics
late Middle English: from whiles + -t as in against.
wiktionary
From whiles + -t. Surface analysis while + -st(“ excrescence”). Cognate with West Frisian wylst(“whilst”). More at whiles.
etymonline
whilst (adv.)
late 14c., from while (q.v.) with adverbial genitive -s-, and unetymological -t (see amidst).
