Almost willing to accept one's captive here (6)
I believe the answer is:
prison
'accept one's captive here' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'almost willing' is the wordplay.
'almost' becomes 'pris' (I can't justify this - if you can you should give a lot more credence to this answer).
'willing' becomes 'on' (I've seen this in other clues).
'pris'+'on'='PRISON'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for prison that I've seen before include "Gaol" , "Eg, Wormwood Scrubs" , "Cooler" , "cage" , "Place of confinement" .)