Waterproof (8)
(Other definitions for anorak that I've seen before include "good on most figures?" , "Garment (worn by boring obsessive?)" , "Zipped jacket with hood attached" , "Mikado's son (G&S)" , "Boringly obsessive person" .)
'waterproof' is the definition.
(I know that waterproof can be written as raincoat)
This is the entire clue.
(Other definitions for raincoat that I've seen before include "protection against the elements" , "Catriona (anag.)" , "which should keep water out" , "Waterproof outer garment" , "Outer garment for Croatian" .)