Lacking in courage (5)
I believe the answer is:
timid
'lacking in courage' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for timid that I've seen before include "Not brave" , "Easily frightened" , "afraid to speak out?" , "Lacking self-confidence" , "Apprehensive and unassertive" .)