More slothful (6)
I believe the answer is:
lazier
'more slothful' is the definition.
('lazy' can be a synonym of 'slothful')
This is all the clue.
(Other definitions for lazier that I've seen before include "More idle" , "More like a couch potato" , "less inclined to work" , "More indolent or slothful" , "More lethargic or sluggish" .)