flat store

noun2

1. •
   A storage facility in which the material stored is simply piled on a floor (as opposed to a bin or silo).

   • In some flat stores a small trough or day silo is located on the perimeter inside the flat store which is also accessed from the outside of the flat store. — 1998
2. •
   (slang) A crooked gambling establishment, such as a casino running rigged or fixed (dishonest) games of chance.

   • He had told me that in the old days in Chicago he had run a flat-store with a partner who had tuberculosis and also smoked cigars. — 1962