A class is a noun: Ball.
An interface is an adjective, usually of the form verb-"able": Serializable. Shootable.
A mixin is a gerund: Serializing. Encrypting.
Too bad there's no mixins in the language I have to speak every day.
Warning: I've got no clue about this stuff, and I'm a learner expressing an analogy that occurred to him which is likely dead wrong.