grinning vs facial gesture

grinning and facial gesture both are nouns.

Word	Noun	Adjective	Verb	Adverb
grinning	Yes	No	No	No
facial gesture	Yes	No	No	No

As nouns, facial gesture is a hypernym of grinning; that is, facial gesture is a word with a broader meaning than grinning:

grinning: a facial expression characterized by turning up the corners of the mouth; usually shows pleasure or amusement
facial gesture: a gesture executed with the facial muscles

Other hypernyms of grinning include facial expression.

grinning (noun)	facial gesture (noun)
a facial expression characterized by turning up the corners of the mouth; usually shows pleasure or amusement	a gesture executed with the facial muscles