Tied, to deter escaping, the captive (8)
I believe the answer is:
tethered
'tied' is the definition.
(thesaurus)
'deter escaping the captive' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'the' is 'eth' which is within the answer.
an anagram of 'deter' is 'tered' which is within the remaining letters.
No letters remain.
This explanation may well be incorrect...
'to' is the link.
Can you help me to learn more?
(Other definitions for tethered that I've seen before include "Restrained with a rope" , "Fastened with rope or chain, like animal" , "on a leash" , "Of animal, with rope fastened to prevent straying" , "Of animal, secured or hobbled" .)