open-class word vs verb

open-class word and verb both are nouns.

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

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

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

Other hyponyms of open-class word include head word, headword, noun, modifier, qualifier, numeral.

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