Source : Webster's Revised Unabridged Dictionary (1913)

Dirk \Dirk\, a. [See {Dark}, a.]
   Dark. [Obs.] --Chaucer.

Dirk \Dirk\, v. t.
   To darken. [Obs.] --Spenser.

Dirk \Dirk\, n. [Ir. duirc.]
   A kind of dagger or poniard; -- formerly much used by the
   Scottish Highlander.

   {Dirk knife}, a clasp knife having a large, dirklike blade.

Dirk \Dirk\, v. t. [imp. & p. p. {Dirked}; p. pr. & vb. n.
   {Dirking}.]
   To stab with a dirk. --Sir W. Scott.

Source : WordNet®

dirk
     n : a long dagger with a straight blade