: professional or official position : occupation : the action for which a person or thing is specially fitted or used or for which a thing exists : purpose : any of a group of related actions contributing to a larger action; especially : the normal and specific contribution of a bodily part to the economy of a living organism : an official or formal ceremony or social gathering a : a mathematical correspondence that assigns exactly one element of one set to each element of the same or another set b : a variable (such as a quality, trait, or measurement) that depends on and varies with another : characteristic behavior of a chemical compound due to a particular reactive unit; also ...