A fatal cast (3)
I believe the answer is:
die
'cast' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for die that I've seen before include "Engraved device that stamps design on coins" , "Cube with spots on the six faces" , "something needed for board game?" , "It may be used in a game" , "Depart with engraved stamp" .)