Ash tree and Downy ash

Ash tree noun - Any of various deciduous pinnate-leaved ornamental or timber trees of the genus Fraxinus.

Downy ash and ash tree are semantically related. In some cases you can replace phrase "Downy ash" with "Ash tree", this phrases are similar.

Downy ash noun - Smallish American tree with velvety branchlets and lower leaf surfaces.

Ash tree and downy ash are semantically related. You can use "Ash tree" instead a noun phrase "Downy ash".