Missing head, slender dart (5)
I believe the answer is:
arrow
'dart' is the definition.
(I've seen this before)
'missing head slender' is the wordplay.
'missing head' means to remove the first letter.
'slender' becomes 'narrow' (similar in meaning).
'narrow' with its initial letter taken away is 'ARROW'.
(Other definitions for arrow that I've seen before include "Mark with pointer" , "Slender, pointed missile" , "Missile for bowman" , "It caught Harold's eye" , "What's shot from a bow" .)