water oak vs Quercus nigra

water oak and Quercus nigra both are nouns.

Word	Noun	Adjective	Verb	Adverb
water oak	Yes	No	No	No
Quercus nigra	Yes	No	No	No

As nouns, water oak and Quercus nigra are synonyms defined as:

water oak and Quercus nigra: relatively tall deciduous water oak of southeastern United States often cultivated as a shade tree; thrives in wet soil

Other synonyms of water oak include possum oak.

water oak (noun)	Quercus nigra (noun)
relatively tall deciduous water oak of southeastern United States often cultivated as a shade tree; thrives in wet soil	relatively tall deciduous water oak of southeastern United States often cultivated as a shade tree; thrives in wet soil