add-on

Noun	1.	add-on - a component that is added to something to improve it; "the addition of a bathroom was a major improvement"; "the addition of cinammon improved the flavor" Synonyms: addition, improver
	2.	add-on - a supplementary component that improves capability Synonyms: appurtenance, accessory, supplement

add on, addition, additive, afterthought, annex, annexe, attachment, component, constituent, element, elongation, extension, improver, wing