whilst
conj.during the same time that something else is happening. It is a more formal way to say 'while'.
conj.during the time that; at the same time as. Used as a formal or literary alternative to 'while', primarily in British English.
“I listened to music whilst I cleaned the house.”
“The researchers observed the subjects' reactions whilst they performed a series of memory tasks under pressure.”
“Whilst the initial results of the study appear promising, the long-term implications of the treatment remain largely unknown and require further investigation.”
Functions as a subordinating conjunction. It is significantly more common in British English than American English and is typically reserved for formal writing.
Whilst is a conjunction and must be followed by a clause or a participle, not a simple noun phrase.
“So we have seen Maresca's City leave four or five players – the three defenders and the holding midfielders – behind the ball whilst they attack, ensuring the team maintain a good 'rest defence'.”
“Whilst schemes like Keighley's can help on the margins, they say, at the national level a much bigger answer is needed.”
From Late Middle English whilst, whilest, qwhilste (Northern England), quilest (Northwest Midlands) [and other forms], from whiles (“during the time that, while; only so long as; provided that; because, since; until”) + -t (excrescent suffix, perhaps due to a combination of -(e)s and the following word the, or influenced by the superlative suffix -est). Whiles is derived from whiles (“period of time, a while”, noun) (probably from the second element of adverbs and conjunctions like otherwhiles and somewhiles), from while (“period of time, a while”, noun) + -s (suffix forming adverbs of manner, space, and time); and while is from Old English hwīl (“period of time, a while”), ultimately from Proto-Germanic hwīlō (“period of time, a while; period of rest, break, pause”), from Proto-Indo-European kʷyeh₁- (“to rest; peace, rest”). The English word can be analysed as whiles + -t (excrescent suffix appended to words suffixed with -s). cognates * West Frisian wylst (“whilst”)
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.