extension course vs class

extension course and class both are nouns.

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

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

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

extension course (noun)	class (noun)
a course offered as part of an extension service	education imparted in a series of lessons or meetings
	elegance in dress or behavior
	a collection of things sharing a common attribute
	people having the same social, economic, or educational status
	(biology) a taxonomic group containing one or more orders
	a body of students who are taught together
	a body of students who graduate together
	a league ranked by quality

extension course (verb)	class (verb)
	arrange or order by classes or categories