Definition of castable:
(adj) :
Able to be cast. In particular:
(adj) :
(engineering) Capable of being cast, as in a mould.
(adj) :
(programming) Capable of being cast to another data type.
(adj) :
Capable of or suitable for being assigned a role in a play, film, etc.
(adj) :
Capable of being performed and brought forth (as a spell or magic).
(n) :
(engineering) Any substance that can be cast, as in a mould.