The name comes from the Scottish Gaelic '. Although the primary meaning of ' is "black", the secondary meaning of "hidden" is at the root of ', based on the stories and theories surrounding the knife's origin, in particular those associated with the Highland custom of depositing weapons at the entrance to a house prior to entering as a guest. Compare also other Gaelic word-formations such as ' "underwater skerry" (lit. black skerry), ' "riddle" (lit. hidden word), ' "enigma" (lit. hidden question).