green ash vs downy ash

green ash and downy ash both are nouns.

Word	Noun	Adjective	Verb	Adverb
green ash	Yes	No	No	No
downy ash	Yes	No	No	No

As nouns, downy ash is a hypernym of green ash; that is, downy ash is a word with a broader meaning than green ash:

green ash: a variety of red ash having glossy branchlets and lower leaf surfaces
downy ash: smallish American tree with velvety branchlets and lower leaf surfaces

Other hypernyms of green ash include Fraxinus pennsylvanica, red ash.

green ash (noun)	downy ash (noun)
a variety of red ash having glossy branchlets and lower leaf surfaces	smallish American tree with velvety branchlets and lower leaf surfaces