facial gesture vs grin

facial gesture and grin both are nouns.

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

As nouns, grin is a hyponym of facial gesture; that is, grin is a word with a more specific, narrower meaning than facial gesture:

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

Other hyponyms of facial gesture include emoticon, gape, face, grimace, frown, scowl, grinning, smile, smiling, laugh, snarl, straight face, wink, wince.

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

facial gesture (verb)	grin (verb)
	to draw back the lips and reveal the teeth, in a smile, grimace, or snarl