sweet gum vs gumwood

sweet gum and gumwood both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet gum	Yes	No	No	No
gumwood	Yes	No	No	No

As nouns, gumwood is a hypernym of sweet gum; that is, gumwood is a word with a broader meaning than sweet gum:

sweet gum: reddish-brown wood and lumber from heartwood of the sweet gum tree used to make furniture
gumwood: wood or lumber from any of various gum trees especially the sweet gum

Other hypernyms of sweet gum include gum.

sweet gum (noun)	gumwood (noun)
a North American tree of the genus Liquidambar having prickly spherical fruit clusters and fragrant sap	wood or lumber from any of various gum trees especially the sweet gum
aromatic exudate from the sweet gum tree
reddish-brown wood and lumber from heartwood of the sweet gum tree used to make furniture