major form class vs word class

major form class and word class both are nouns.

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

As nouns, word class is a hypernym of major form class; that is, word 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
word class: one of the traditional categories of words intended to reflect their functions in a grammatical context

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

major form class (noun)	word 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