extension course vs course

extension course and course both are nouns.

Word	Noun	Adjective	Verb	Adverb
extension course	Yes	No	No	No
course	Yes	No	Yes	Yes

As nouns, course is a hypernym of extension course; that is, course is a word with a broader meaning than extension course:

Other hypernyms of extension course include class, course of instruction, course of study.

extension course (noun)	course (noun)
a course offered as part of an extension service	a mode of action
	education imparted in a series of lessons or meetings
	facility consisting of a circumscribed area of land or water laid out for a sport
	(construction) a layer of masonry
	part of a meal served at one time
	a connected series of events or actions or developments
	a body of students who are taught together
	general line of orientation
	a line or route along which something travels or moves

extension course (adverb)	course (adverb)
	as might be expected