oxbow vs terra firma

oxbow and terra firma both are nouns.

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

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

Other hypernyms of oxbow include dry land, earth, ground, land, solid ground.

oxbow (noun)	terra firma (noun)
a wooden framework bent in the shape of a U; its upper ends are attached to the horizontal yoke and the loop goes around the neck of an ox	the solid part of the earth's surface
a U-shaped curve in a stream
the land inside an oxbow bend in a river