Beastly idleness (5)
I believe the answer is:
sloth
'idleness' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for sloth that I've seen before include "Deadly offence" , "Arboreal animal" , "Aversion to industry" , "Sinful" , "reluctance to work" .)