They're quite dishonourable to claim it's been taken from cadavers (4)
I believe the answer is:
cads
'cadavers' is the definition.
Although both the answer and definition are plural nouns, I can't see how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for cads that I've seen before include "'Blackguards, bounders (4)'" , "Knaves" , "Rotters" .)