adv

• (archaic or obsolete except dialectal) Often preceded by the: During the time; meanwhile.
  "Nay, I prethee put on this gown, & this beard, make him beleeue thou art ſir Topas the Curate, doe it quickly. Ile call ſir Toby the whilſt."

conj

• (UK, Ireland, Commonwealth, literary or somewhat rare in North America) Synonym of while.
  "Drivers must switch off engines whilst on stand."
• (UK, Ireland, Commonwealth, literary or somewhat rare in North America) Synonym of while.
  "[P]ray, step down to the cellar and fetch us a bottle of the Burgundy, 1678—it is the fourth bin from the right-hand turn—And I say, Craigie—you may fetch up half-a-dozen whilst you are about it—Egad, we'll make a night on't."
• (UK, Ireland, Commonwealth, literary or somewhat rare in North America) Synonym of while.
  "His company must do his minions grace, / Whil'ſt I at home ſtarue for a merrie looke: / Hath homelie age th'alluring beauty tooke / From my poore cheeke?"
• (UK, Ireland, Commonwealth, literary or somewhat rare in North America) Synonym of while.
  "Modern engine sheds of advanced design have also been built at Radyr, Abercynon, and elsewhere, whilst other depots have been remodelled and re-equipped."