Catkin

Those fluffy puffs (not a breakfast cereal) on the branches of various trees and shrubs are called catkins.  The word catkin is a derivative of the Dutch katteken, meaning "kitten," from their quasi-resemblance to a cat's tail.   The fact that they are found on, amongst others, the pussy willow, is... not exactly a coincidence, but neither is it directly connected.  The word "catkin" was around in England for approximately 300 years before the willow (genus Salix) was named in the US, for example.  It might best be described as a case of parallel linguistic evolution-- the flower clusters in question (for that is what they are) were named because they resembled a cat's tail, and the pussy willow tree was named, well, because it has growths that resemble a cat's tail.  So pussy willows have catkins not because someone was trying to be especially clever, but just because some descriptions are fairly universal.

Oh, and the technical name for a catkin is an ament.  Interestingly, they have also been called aglets (their true purpose is sinister).