Turn black before death (4)
I believe the answer is:
bend
'turn' is the definition.
(bending is a kind of turning)
'black before death' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'before' says to put letters next to each other.
'death' becomes 'end' (synonyms).
'b'+'end'='BEND'
(Other definitions for bend that I've seen before include "Curve; knot" , "Knot; heraldic stripe" , "Corner" , "It may be sinister" , "Turn, flex" .)