subjoining vs expansion

subjoining and expansion both are nouns.

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

As nouns, expansion is a hypernym of subjoining; that is, expansion is a word with a broader meaning than subjoining:

Other hypernyms of subjoining include expanding upon.

subjoining (noun)	expansion (noun)
the act of supplementing	the act of increasing (something) in size or volume or quantity or scope
	adding information or detail
	a discussion that provides additional information
	a function expressed as a sum or product of terms