chewing vs gumming

chewing and gumming both are nouns.

Word	Noun	Adjective	Verb	Adverb
chewing	Yes	No	No	No
gumming	Yes	No	No	No

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

chewing: biting and grinding food in your mouth so it becomes soft enough to swallow
gumming: ineffectual chewing (as if without teeth)

Other hyponyms of chewing include chomping, mumbling, rumination.

chewing (noun)	gumming (noun)
biting and grinding food in your mouth so it becomes soft enough to swallow	ineffectual chewing (as if without teeth)