The Collaborative International Dictionary of English v.0.48:

Fitch \Fitch\ (?; 224), n.; pl. Fitches. [See Vetch.]
   1. (Bot.) A vetch. [Obs.]
      [1913 Webster]

   2. pl. (Bot.) A word found in the Authorized Version of the
      Bible, representing different Hebrew originals. In Isaiah
      xxviii. 25, 27, it means the black aromatic seeds of
      Nigella sativa, still used as a flavoring in the East.
      In Ezekiel iv. 9, the Revised Version now reads spelt.
      [1913 Webster]

Easton's 1897 Bible Dictionary:

Fitches
   (Isa. 28:25, 27), the rendering of the Hebrew _ketsah_, "without
   doubt the Nigella sativa, a small annual of the order
   Ranunculacece, which grows wild in the Mediterranean countries,
   and is cultivated in Egypt and Syria for its seed." It is
   rendered in margin of the Revised Version "black cummin." The
   seeds are used as a condiment.

     In Ezek. 4:9 this word is the rendering of the Hebrew
   _kussemeth_ (incorrectly rendered "rye" in the Authorized
   Version of Ex. 9:32 and Isa. 28:25, but "spelt" in the Revised
   Version). The reading "fitches" here is an error; it should be
   "spelt."