Long dagger (8)
I believe the answer is:
stiletto
'long dagger' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for stiletto that I've seen before include "Slender-bladed dagger - heel" , "High-heeled shoe" , "Possible cause of stabbing pains" , "Tapering dagger" , "Dagger; tapered heel" .)