upper bound vs boundary

upper bound and boundary both are nouns.

Word	Noun	Adjective	Verb	Adverb
upper bound	Yes	No	No	No
boundary	Yes	No	No	No

As nouns, boundary is a hypernym of upper bound; that is, boundary is a word with a broader meaning than upper bound:

upper bound: (mathematics) a number equal to or greater than any other number in a given set
boundary: a line determining the limits of an area

Other hypernyms of upper bound include bound, edge.

upper bound (noun)	boundary (noun)
(mathematics) a number equal to or greater than any other number in a given set	the greatest possible degree of something
	the line or plane indicating the limit or extent of something
	a line determining the limits of an area