Biological BRISTLE is a type of hair found on the bodies of some animals, such as cats and dogs. It is made up of a stiff, hollow shaft with a pointed tip. The term 'Biological BRISTLE' is derived from the Latin word 'SETA', which means 'BRISTLE'. SETA is the four-letter answer to this crossword puzzle. Biological Bristles are used for protection, insulation, and sensory purposes. They are also used in grooming and cleaning.