Stern edge is behind front of galley (4)
I believe the answer is:
grim
'stern' is the definition.
(I know that stern can be written as grim)
'edge is behind front of galley' is the wordplay.
'edge' becomes 'rim' (rim is a kind of edge).
'is behind' says to put letters next to each other.
'front of' indicates taking the first letters.
The initial letter of 'galley' is 'g'.
'rim' put after 'g' is 'GRIM'.
(Other definitions for grim that I've seen before include "Stern and unsmiling" , "Frightful" , "The - Reaper is death" , "Unrelentingly harsh" , "Severe; horrible" .)