extent vs boundary

extent and boundary both are nouns.

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

As nouns, boundary is a hyponym of extent; that is, boundary is a word with a more specific, narrower meaning than extent:

extent (noun)	boundary (noun)
the distance or area or volume over which something extends	the greatest possible degree of something
the point or degree to which something extends	the line or plane indicating the limit or extent of something
	a line determining the limits of an area