supplementation vs subjoining

supplementation and subjoining both are nouns.

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

As nouns, supplementation and subjoining are synonyms defined as:

Other synonyms of supplementation include subjunction.

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