frown vs grimace

frown and grimace both are nouns.

Word	Noun	Adjective	Verb	Adverb
frown	Yes	No	Yes	No
grimace	Yes	No	Yes	No

As verbs, grimace is a hypernym of frown; that is, grimace is a word with a broader meaning than frown:

frown: look angry or sullen, wrinkle one's forehead, as if to signal disapproval
grimace: contort the face to indicate a certain mental or emotional state

Other hypernyms of frown include make a face, pull a face.

frown (noun)	grimace (noun)
a facial expression of dislike or displeasure	a contorted facial expression

frown (verb)	grimace (verb)
look angry or sullen, wrinkle one's forehead, as if to signal disapproval	contort the face to indicate a certain mental or emotional state