The name comes from the Gaelic sgian-dubh. Although the primary meaning of dubh is "black", the secondary meaning of "hidden" is at the root of sgian-dubh, 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 dubh-sgeir "underwater skerry" (lit. black skerry), dubh-fhacal "riddle" (lit. hidden word), dubh-cheist "enigma" (lit. hidden question).