Heartless poacher occasionally ties down captives here (6)
I believe the answer is:
prison
'captives here' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'heartless poacher occasionally ties down' is the wordplay.
'heartless' means to remove the middle letters.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'poacher' with its middle taken out is 'pr'.
'ties'+'down'='tiesdown'
The alternating letters of 'tiesdown' are 'ison'.
'pr'+'ison'='PRISON'
Can you help me to learn more?
(Other definitions for prison that I've seen before include "Stir - can" , "Place of incarceration" , "porridge" , "Gaol" , "Correctional institution" .)