Description of big effort in situation with no one at work? (3-3)

I believe the answer is:

all-out

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'at work?' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I don't see?

I cannot understand how the remainder of the clue works.

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(Other definitions for all-out that I've seen before include "At full speed - no one at home" , "Whole-hearted (effort)" , "Nobody home, at top speed" , "Complete" , "Using full strength or energy - nobody home?" .)

I've seen this clue in The Guardian.

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