maximum vs boundary

maximum and boundary both are nouns.

Word	Noun	Adjective	Verb	Adverb
maximum	Yes	Yes	No	No
boundary	Yes	No	No	No

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

Other hypernyms of maximum include bound, limit.

maximum (noun)	boundary (noun)
the greatest possible degree	the greatest possible degree of something
the point on a curve where the tangent changes from positive on the left to negative on the right	the line or plane indicating the limit or extent of something
the largest possible quantity	a line determining the limits of an area

maximum (adjective)	boundary (adjective)
the greatest or most complete or best possible