subjoining vs supplementation

subjoining and supplementation both are nouns.

Word	Noun	Adjective	Verb	Adverb
subjoining	Yes	No	No	No
supplementation	Yes	No	No	No

As nouns, subjoining and supplementation are synonyms defined as:

Other synonyms of subjoining include subjunction.

subjoining (noun)	supplementation (noun)
the act of supplementing	the act of supplementing
	a quantity added (e.g. to make up for a deficiency)