Sluggishness I retain at work (7)
I believe the answer is:
inertia
'sluggishness' is the definition.
(thesaurus)
'i retain at work' is the wordplay.
'at work' indicates anagramming the letters.
'retain' with letters rearranged gives 'nertia'.
'i'+'nertia'='INERTIA'
(Other definitions for inertia that I've seen before include "I retain, being without energy" , "Disposition to do nothing" , "Way of selling" , "I retain (anag) - the tendency to retain same speed and direction" , "Slowness to act, lassitude" .)