Used to say that two things happen at the same time, or to contrast two ideas. It can also be a noun meaning a short period of time.
From Old English 'hwīl', meaning 'a period of time.' It shifted from being mostly a time word to also joining clauses, similar to 'as' or 'although.'
A simple time word grew into a powerful connector of ideas. 'While' quietly does double duty: it tells you when and also how ideas differ.
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