The Collaborative International Dictionary of English v.0.48:

Grist \Grist\, n. [AS. grist, fr. grindan. See Grind.]
   [1913 Webster]
   1. Ground corn; that which is ground at one time; as much
      grain as is carried to the mill at one time, or the meal
      it produces.
      [1913 Webster]

            Get grist to the mill to have plenty in store.
                                                  --Tusser. Q.
      [1913 Webster]

   2. Supply; provision. --Swift.
      [1913 Webster]

   3. In rope making, a given size of rope, common grist being a
      rope three inches in circumference, with twenty yarns in
      each of the three strands. --Knight.
      [1913 Webster]

   All is grist that comes to his mill, all that he has
      anything to do with is a source of profit. [Colloq.]

   To bring grist to the maill, to bring profitable business
      into one's hands; to be a source of profit. [Colloq.]
      --Ayliffe.
      [1913 Webster]

WordNet (r) 3.0 (2006):

grist
    n 1: grain intended to be or that has been ground