Coup, induced almost entirely in error, is doing nothing (10)
I believe the answer is:
unoccupied
'doing nothing' is the definition.
(both can mean free or not busy)
'coup induced almost entirely in error' is the wordplay.
'almost entirely' means to remove the last letter.
'in error' indicates an anagram.
'coup'+'induced'='coupinduced'
'coupinduced' with its final letter taken off is 'coupinduce'.
'coupinduce' anagrammed gives 'UNOCCUPIED'.
'is' is the link.
(Other definitions for unoccupied that I've seen before include "Empty" , "idle" , "Not tenanted" .)