black ash vs Fraxinus nigra

black ash and Fraxinus nigra both are nouns.

Word	Noun	Adjective	Verb	Adverb
black ash	Yes	No	No	No
Fraxinus nigra	Yes	No	No	No

As nouns, black ash and Fraxinus nigra are synonyms defined as:

black ash and Fraxinus nigra: vigorous spreading North American tree having dark brown heavy wood; leaves turn gold in autumn

Other synonyms of black ash include basket ash, brown ash, hoop ash.

black ash (noun)	Fraxinus nigra (noun)
vigorous spreading North American tree having dark brown heavy wood; leaves turn gold in autumn	vigorous spreading North American tree having dark brown heavy wood; leaves turn gold in autumn