Caolhain Share definition Flag The Scottish word for dog. A Caolhain is a friend, trusting, trustworthy, reliable, and almost selflessly loyal. Pronounced Cool-lane. Dude, Sean is such a Caolhain! Caolhain by BoydClansman April 20, 2010 0 0 Get merch Get the Caolhain mug. Buy Now — $32.95 See more merch