D defs.my
Entry 3 senses Webster, 1913

Grist

/grĭst/ · IPA /ɡɹɪst/
01 n. 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.
  1. 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.
    “Get grist to the mill to have plenty in store.” — Tusser. Q.
  2. 2.
    Supply; provision.
  3. 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.
Phrases & compounds
All is grist that comes to his mill — all that he has anything to do with is a source of profit.
To bring grist to the maill — to bring profitable business into one's hands; to be a source of profit.