A catkin is a long, soft flower that hangs from a twig, often in little groups. You see them in spring on trees such as willow, birch, hazel, and poplar: yellow with pollen, or grey-green, and if you rub them they feel like fine fur. People thought the longer ones looked like a small cat’s tail — or like cat fur — and that is how the name arose. It is a gentle nature word: gardeners, biology class, poems. It is not slang. Botany has a colder name, ament, but learners almost always hear catkin. Though actually the fluffy stuff that flies off a willow later is not the catkin itself; the catkin is the hanging flower, and the flying fluff is seed.

柔荑花序（柳、樺上吊下來那串軟花；不是後來滿天飛的柳絮）