Three-pronged spear
I believe the answer is:
trident
I believe this is a double definition.
'three' is the first definition.
(thesaurus)
'pronged spear' is the second definition.
(I've seen this before)
(Other definitions for trident that I've seen before include "Red tint? (anagram)" , "Britannia's weapon" , "Neptune's fork" , "Nuclear weapon" , "Submarine missile" .)