elongation vs add-on

elongation and add-on both are nouns.

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

As nouns, add-on is a hypernym of elongation; that is, add-on is a word with a broader meaning than elongation:

Other hypernyms of elongation include addition, improver.

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