add-on vs elongation

add-on and elongation both are nouns.

Word	Noun	Adjective	Verb	Adverb
add-on	Yes	No	No	No
elongation	Yes	No	No	No

As nouns, elongation is a hyponym of add-on; that is, elongation is a word with a more specific, narrower meaning than add-on:

Other hyponyms of add-on include additive, afterthought, annex, annexe, extension, wing, attachment, extension.

add-on (noun)	elongation (noun)
a component that is added to something to improve it	the act of lengthening something
a supplementary component that improves capability	an addition to the length of something
a software module that extends or enhances the capabilities of an existing application	the quality of being elongated