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while

A conjunction:
            while the dog slept ...

Avoid using while to mean though or whereas when there is a danger of ambiguity:
            Incorrect:    While most Canadians speak English, the Quebecois speak French
            Write:             Though most Canadians ...

Do not confuse the adverb awhile with the noun phrase a while:
            awhile: adverb—We stood awhile on the dock; awhile back.
             a while: article and noun—We stood for a while on the dock; a while ago; wait a while.

Note: not whilst