uninstantiable

As an adjective uninstantiable

is not instantiable; that cannot be instantiated.

As a noun mixin is

in object-oriented programming, an uninstantiable class that provides functionality to be inherited by a subclass.

As a verb instantiate

is to represent (something) by a concrete instance.

As an adjective uninstantiable is

not instantiable; that cannot be instantiated.

As adjectives the difference between instantiable and uninstantiable

is that instantiable is that can be instantiated while uninstantiable is not instantiable; that cannot be instantiated.