wood vs rain forest

wood and rain forest both are nouns.

Word	Noun	Adjective	Verb	Adverb
wood	Yes	No	No	No
rain forest	Yes	No	No	No

As nouns, rain forest is a hyponym of wood; that is, rain forest is a word with a more specific, narrower meaning than wood:

wood (noun)	rain forest (noun)
any wind instrument other than the brass instruments	a forest with heavy annual rainfall
a golf club with a long shaft used to hit long shots; originally made with a wooden head
the trees and other plants in a large densely wooded area
the hard fibrous lignified substance under the bark of trees