Engaged just one in a whole group (5)

I believe the answer is:

hired

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'engaged' is the definition.
('hire' can be a synonym of 'engage')

I can't explain the rest of the clue.

(Other definitions for hired that I've seen before include "Chartered" , "Taken into service" , "Paid to work" , "like a Merc" , "Employed for wages" .)

I've seen this clue in the Evening Standard.

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