Hostage-taker in cover by hill (6)
I believe the answer is:
captor
'hostage-taker' is the definition.
I can't tell whether this defines the answer.
'cover by hill' is the wordplay.
'cover' becomes 'cap' (cap is a kind of cover).
'by' is a charade indicator (letters next to each other).
'hill' becomes 'tor' (tor is a kind of hill).
'cap'+'tor'='CAPTOR'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for captor that I've seen before include "Someone taking prisoner" , "One who confines another" , "One confining another" , "Person who takes and holds" , "Person who has taken another prisoner" .)