verb vs open-class word

verb and open-class word both are nouns.

Word	Noun	Adjective	Verb	Adverb
verb	Yes	No	No	No
open-class word	Yes	No	No	No

As nouns, open-class word is a hypernym of verb; that is, open-class word is a word with a broader meaning than verb:

verb: a content word that denotes an action, occurrence, or state of existence
open-class word: a word to which an independent meaning can be assigned

Other hypernyms of verb include content word.

verb (noun)	open-class word (noun)
a content word that denotes an action, occurrence, or state of existence	a word to which an independent meaning can be assigned
the word class that serves as the predicate of a sentence