Pussy willow and Willow tree

Pussy willow noun - Small willow of eastern North America having greyish leaves and silky catkins that come before the leaves.

Willow tree and pussy willow are semantically related. In some cases you can use "Willow tree" instead a noun phrase "Pussy willow".

Willow tree noun - Any of numerous deciduous trees and shrubs of the genus Salix.

Pussy willow and willow tree are semantically related. Sometimes you can replace phrase "Pussy willow" with "Willow tree", this phrases are similar.