Discharge Manx cat? (3)
I believe the answer is:
pus
'discharge' is the definition.
(discharge from the body)
'manx cat?' is the wordplay.
'manx' means to remove the last letter (Manx cats have no tail).
'cat?' becomes 'puss' (puss is a kind of cat).
'puss' with its final letter taken away is 'PUS'.
(Other definitions for pus that I've seen before include "Fluid in infected tissue" , "Material in wounds" , "Yellow matter formed in infected wound" , "Fluid, a product of inflammation" , "Liquid produced in infected tissue" .)