Kinds are types for types. Kinds are simple, having a name and potentially some parameters. Types have exactly one Kind. Terms can have multiple Types, so they can have multiple Kinds. Types are attached with a single colon. Kinds are attached with a double colon. There are 3 builtin Kinds: Term, Constant, and Nil. New kinds do not need to be defined before they are used.
5 : Prime :: Term; 2 : Second :: Unit; 1 :  :: Constant; 3 :  + Integer + Second :: Constant + Term + Unit;