Captious, carping (8)
I believe the answer is:
critical
This clue is a double definition.
'captious' is the first definition.
(similar in meaning)
'carping' is the second definition.
(similar in meaning)
(Other definitions for critical that I've seen before include "giving literary analysis" , "of such crucial importance" , "Finding faults" , "Making negative judgments" , "essential" .)