class vs junior class

class and junior class both are nouns.

Word	Noun	Adjective	Verb	Adverb
class	Yes	No	Yes	No
junior class	Yes	No	No	No

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

Other hyponyms of class include graduating class, senior class, sophomore class, freshman class.

class (noun)	junior class (noun)
education imparted in a series of lessons or meetings	penultimate class in high school or college
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

class (verb)	junior class (verb)
arrange or order by classes or categories