Deny old prison contains no women (6)
I believe the answer is:
negate
'deny' is the definition.
(negate can mean to deny or refute)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for negate that I've seen before include "Contradict" , "Cause to have no effect" , "Age ten (anag)" , "Countermand" , "Nullify - deny the existence of" .)