From the simple and elegant to highly ornate pieces Sgian Dubh were once a part of everyday life in Scotland. The name means “black knife” which has been mistakenly though to hint at nefarious purposes. In reality though it was used for eating and defensive purposes. The knife was generally carried hidden or “in the dark” hence “black” and as far as I’m aware this was under the arm. On entering a house it was taken from its carrying position and tucked into the sock so it could be seen by your host and thereby “proving” you had no hostile intention. If you know anything about Scottish history though you will be aware that didn’t always work.
Today the Sgian Dubh is carried in the sock as part of a kilt outfit.