Prisoner in horrible pit in cave (7)
I believe the answer is:
captive
'prisoner' is the definition.
(I know that prisoner can be written as captive)
'horrible pit in cave' is the wordplay.
'horrible' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'pit' with letters rearranged gives 'pti'.
'pti' going inside 'cave' is 'CAPTIVE'.
'in' acts as a link.
(Other definitions for captive that I've seen before include "Prisoner" , "Detainee" .)