What does "catkin" mean?

Catkin: An ament; a species of inflorescence, consisting of a slender axis with many unisexual apetalous flowers along its sides, as in the willow and poplar, and (as to the staminate flowers) in the chestnut, oak, hickory, etc. -- so called from its resemblance to a cat's tail. See Illust. of Ament.