whilst

• whilest (obsolete)
• whylst (obsolete)
• whylest (obsolete)

From whiles +‎ -t. Surface analysis while +‎ -st (“excrescence”). Cognate with West Frisian wylst (“whilst”). More at whiles.

• (General American, Received Pronunciation) IPA^(key): /waɪlst/, /hwaɪlst/

• Audio (US)

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whilst

1. (Britain, rare or literary in North America) While, at the same time.
   • 1963, Margery Allingham, chapter 17, in The China Governess‎:

     The face which emerged was not reassuring. It was blunt and grey, the nose springing thick and flat from high on the frontal bone of the forehead, whilst his eyes were narrow slits of dark in a tight bandage of tissue. […].

• Mostly restrained to use in British English.
• Rare in North America and may be considered archaic, pedantic or pompous.

• while

• while on Wikipedia.Wikipedia
• whilst in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.
• “whilst” in Douglas Harper, Online Etymology Dictionary, 2001–2019.