Someone lacking courage (6)
I believe the answer is:
coward
'someone lacking courage' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for coward that I've seen before include "Noel ..... composed musical 'Bitter Sweet'" , "Person who shows fear or timidity" , "Chicken" , "Person who is deficient in courage" , "wimp" .)