cairn terrier, breed of small working terrier developed on the Isle of Skye in the 19th cent. It stands about 10 in. (25 cm) high at the shoulder and weighs about 14 lb (6.4 kg). The weather-resistant double coat consists of a soft, furry underlayer and a profuse, hard outercoat about 2 in. (5 cm) long. It may be any color except white, often with dark ears, muzzle, and tip of tail. Originally bred to rout fur-bearing vermin from the rocky crags and cliffs of its native island, the cairn was also bred as a water dog to hunt otters. At an early stage in its history it was accepted into the household as a companion and watchdog, the roles for which it is principally raised today. See dog.