DIRK, a dagger, particularly the heavy dagger carried by the Highlanders of Scotland. The dirk as worn in full Highland costume is an elaborately ornamented weapon, with cairngorms or other stones set in the head of the handle, which has no guard. Inserted in the sheath there may be two small knives. The dirk, in the shape of a straight blade, with a small guard, some 18 in. long, is worn by midshipmen in the British navy. The origin of the word is doubtful. The earlier forms were dork and durk, and the spelling dirk, adopted by Johnson, represents the pronunciation of the second form. The name seems to have been early applied to the daggers of the Highlanders, but the Gaelic word is biodag, and the Irish duirc, often stated to be the origin, is only an adaptation of the English word. It may be a corruption of the German Dolch, a dagger. The suggestion that it is an application of the Christian name "Dirk," the short form of "Dieterich," is not borne out, according to the New English Dictionary, by any use of this name for a dagger, and is further disproved by the earlier English spelling.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)