Torpid (8)
'torpid' is the definition.
(synonyms)
This is all the clue.
(Other definitions for sluggish that I've seen before include "Torpid" , "Hardly speeding" , "Slow-moving like garden mollusc" , "Lethargic" , "like a bullet?" .)
(Other definitions for idle that I've seen before include "Not used to work" , "Do nothing, laze" , "Avoiding work, lazy" , "Not busy" , "Monty Python's Eric, b. 1943" .)