grinning vs smirk

grinning and smirk both are nouns.

Word	Noun	Adjective	Verb	Adverb
grinning	Yes	No	No	No
smirk	Yes	No	Yes	No

As nouns, smirk is a hyponym of grinning; that is, smirk is a word with a more specific, narrower meaning than grinning:

grinning: a facial expression characterized by turning up the corners of the mouth; usually shows pleasure or amusement
smirk: a smile expressing smugness or scorn instead of pleasure

Other hyponyms of grinning include simper.

grinning (noun)	smirk (noun)
a facial expression characterized by turning up the corners of the mouth; usually shows pleasure or amusement	a smile expressing smugness or scorn instead of pleasure

grinning (verb)	smirk (verb)
	smile affectedly or derisively