Baleen is a type of filter-feeding system used by certain species of whales. It consists of plates of keratin, a protein found in hair and nails, that hang from the upper jaw of the WHALE. Baleen is used to strain small prey such as krill and plankton from the water. The term 'baleen' is derived from the Latin word balæna, meaning 'WHALE'. The related terms 'WHALEBONE' (9 letters) and sei (3 letters) refer to two species of whales that use baleen to feed, while 'WHALE' (5 letters) is a general term for any species of cetacean that uses baleen.