Lacking courage (5,7)
(Other definitions for spineless that I've seen before include "Lily-livered" , "Craven, lacking vertebrae" , "Weak, without purpose" , "like tattered old book" , "Lacking (moral) courage" .)
'lacking courage' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for timid that I've seen before include "not forward" , "Lacking in confidence" , "Lacking self-confidence" , "Easily scared" , "Nervous and easily alarmed" .)
(Another definition for faint hearted that I've seen is " Timid".)