smile vs grimace

smile and grimace both are nouns.

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

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

smile: change one's facial expression by spreading the lips, often to signal pleasure
grimace: contort the face to indicate a certain mental or emotional state

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

smile (noun)	grimace (noun)
a facial expression characterized by turning up the corners of the mouth; usually shows pleasure or amusement	a contorted facial expression

smile (verb)	grimace (verb)
change one's facial expression by spreading the lips, often to signal pleasure	contort the face to indicate a certain mental or emotional state
express with a smile