Critic Rex ____ (4)
I believe the answer is:
reed
'critic rex' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for reed that I've seen before include "Vibrator in the mouthpiece of a wind instrument" , "Blade of tall marsh grass" , "Film director" , "Vibrating part of some instruments" , "Grass of marshy land" .)