Cowardly little devil gripped by desire (7)
I believe the answer is:
wimpish
'cowardly' is the definition.
'little devil gripped by desire' is the wordplay.
'little devil' becomes 'imp' (I've seen this before).
'gripped by' is an insertion indicator.
'desire' becomes 'wish' (wishing is a kind of desiring).
'imp' put into 'wish' is 'WIMPISH'.
(Other definitions for wimpish that I've seen before include "Spineless" , "wet!" , "Pathetically feeble" , "Weak" .)