Elephant's tooth (4)
I believe the answer is:
tusk
'elephant's tooth' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tusk that I've seen before include "Long protruding tooth" , "Ivory-coloured dentine" , "Elephant's dentine" , "Protruding ivory, of elephant say" , "Elongated tooth" .)