Pusillanimous (6)
'pusillanimous' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for craven that I've seen before include "Lacking courage, cowardly" , "Cowardly, spineless" , "Faint-hearted" , "Cowardly, abjectly afraid" , "Yellow" .)
(Other definitions for nerveless that I've seen before include "Feeble" , "no feeling" , "Without fear" , "Not able to feel" , "Having great confidence" .)