forest vs terra firma

forest and terra firma both are nouns.

Word	Noun	Adjective	Verb	Adverb
forest	Yes	No	Yes	No
terra firma	Yes	No	No	No

As nouns, terra firma is a hypernym of forest; that is, terra firma is a word with a broader meaning than forest:

Other hypernyms of forest include biome, dry land, earth, ground, land, solid ground.

forest (noun)	terra firma (noun)
the trees and other plants in a large densely wooded area	the solid part of the earth's surface
land that is covered with trees and shrubs

forest (verb)	terra firma (verb)
establish a forest on previously unforested land