voice over vs vocalism

voice over and vocalism both are nouns.

Word	Noun	Adjective	Verb	Adverb
voice over	Yes	No	No	No
vocalism	Yes	No	No	No

As nouns, vocalism is a hypernym of voice over; that is, vocalism is a word with a broader meaning than voice over:

voice over: the voice on an unseen commentator in a film of television program
vocalism: the sound made by the vibration of vocal folds modified by the resonance of the vocal tract

Other hypernyms of voice over include phonation, vocalisation, vocalization, voice, vox.

voice over (noun)	vocalism (noun)
the voice on an unseen commentator in a film of television program	the sound made by the vibration of vocal folds modified by the resonance of the vocal tract
	the system of vowels used in a particular language