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
see also:
grind all is grist that comes to his mill to bring grist to the maill