Defensible (7)
I believe the answer is:
tenable
'defensible' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tenable that I've seen before include "Capable of being kept" , "Able to be believed" , "Able to be defended against attack or objection" , "Of argument, rational and defensible" , "Able to be held" .)