major form class vs form class

major form class and form class both are nouns.

Word	Noun	Adjective	Verb	Adverb
major form class	Yes	No	No	No
form class	Yes	No	No	No

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

major form class: any of the major parts of speech of traditional grammar
form class: one of the traditional categories of words intended to reflect their functions in a grammatical context

Other hypernyms of major form class include part of speech, word class.

major form class (noun)	form class (noun)
any of the major parts of speech of traditional grammar	one of the traditional categories of words intended to reflect their functions in a grammatical context