Addon

Part of speech: noun

Definitions

1. A software module that adds new features or functions to an existing program ; an extra part or item that supplements or enhances the main product or system
2. An extra piece of software designed to extend or improve a computer application ; a supplementary element added to enhance or expand something
3. A supplementary program component that provides additional capabilities ; an accessory or extra feature added to something to increase its utility

Etymology: "Add-on" is a compound built from the phrasal verb "add on," meaning to attach something to something else. The noun was formed from that verb phrase, so the word is a deverbal noun: a thing that is the result of adding on. Its sense has shifted from the physical act of attaching a part to a larger whole toward the software sense of a module that extends an existing program, though the core idea of something bolted onto a main object remains the same.

Synonyms: extension, supplement, addition