Four gills is a term used to describe a type of fish that has four gill slits on each side of its head. This type of fish is found in many different species, including sharks, rays, and skates. The term 'four gills' is derived from the fact that these fish have four gill slits, which are openings in the side of the head that allow the fish to breathe underwater. The crossword solution for the term 'four gills' is 'pint, ' which is a unit of measurement equal to one-eighth of a gallon.