The Collaborative International Dictionary of English v.0.48:
Grist \Grist\, n. [AS. grist, fr. grindan. See Grind.]
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
Get grist to the mill to have plenty in store.
2. Supply; provision. --Swift.
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.
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.]