Parking on the edge? Hash is made of it (4)
I believe the answer is:
hemp
'hash is made of it' is the definition.
(plant from which hashish is made)
'parking on the edge?' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'on' says to put letters next to each other.
'the edge?' becomes 'hem' (I've seen this in another clue).
'p' after 'hem' is 'HEMP'.
(Other definitions for hemp that I've seen before include "Cannabis sativa" , "Marijuana" , "Plant fibre used to make rope" , "Rope, cannabis, plant" , "Source of drug" .)