(transitive) To join or unite (e.g. one thing to another, or as several particulars) so as to increase the number, augment the quantity, or enlarge the magnitude, or so as to form into one aggregate.

(radio) The addition of a song to a station's playlist. / (computer science) An act or instance of adding. / (video games) An additional enemy that joins a fight after the primary target.

Initialism of attention deficit disorder. / Initialism of accidental death and dismemberment.

(sometimes attributive) Something which can be appended to something else.

(transitive) To incorporate (something extra, often an amount of money) into something else (often a bill). / (intransitive) To put an expansion onto a building, usually a home.

Alternative form of add-on

Obsolete spelling of add

(computing) A plug-in.

(law) Abbreviation of addendum.

plural of add