What is the name of the long dagger sometimes worn as part of the formal Scottish Highland dress?

hibees18750, Sgian dubh and Dirk are different weapons; Sgian dubh is a short, single-edged knife, whilst dirk is long usually double-edged dagger. with a blade around 12" long. You wouldn't want to put one of them down your sock.

Jo, it must be the effect of the full moon but I keep laughing out loud from some comments. It feels good to laugh!