A word that has little meaning when standing alone, but instead serves to express grammatical relationships with other words within a sentence, or specify the attitude or mood of the speaker, such as prepositions, pronouns, auxiliary verbs, or conjunctions.
A function word.
A function object.
A structure allowing a function to apply within a generic type, in a way that is conceptually similar to a functor in category theory.
A category homomorphism; a morphism from a source category to a target category which maps objects to objects and arrows to arrows, in such a way as to preserve domains and codomains (of the arrows) as well as composition and identities.