While - whiles - whilst

Whilst is essentially a variant spelling of while, the conjunction meaning 'during [the time that]' (as in the saying "‘while there's life there's hope") or 'at the same time as' (e.g. "While he was boiling the eggs, she was buttering the toast"). There is no practical reason for choosing one form or the other - the choice is a matter of style, and is partly a matter of a native speaker's aesthetic feeling about the sound[s] of the word[s] in a given context

Both whilst and while were previously also used as adverbs and even prepositions or adjectives. There was even a third form, whiles, still current in Scotland, if a trifle old-fashioned. In Scots, both whiles and whilst can be adverbs meaning approximately 'sometimes'.

In academic writing, while (and occasionally whilst) can be used as a conjunction of concession, similar to 'although': "While you may be right in detail, you are not right in general."

Students in Hull (and other places in the North of England) should be aware of a local dialect usage which is different from Standard English. This is to use while to mean something like the Standard 'until'. It can be confusing: consider the consequences of the different meanings of a notice at a pedestrian crossing which says: 'Do not cross while red man is flashing'. A dialect speaker may read this

• you should not cross the road until you can see the red man flashing

while the Standard English interpretation is that

• you should not cross the road when you can see the red man flashing.

Thus the Hull interpretation is the opposite of the Standard English meaning - and very dangerous!

Two cognate words, both essentially obsolete although still to be seen, derived from while are:

• whilom. This meant originally 'at times', and later, adverbially, 'at some time past' and adjectivally 'former', and, of people, 'late', 'deceased'.
• erstwhile. This meant 'some while ago', 'formerly'.

For a common typing mistake, see whist.