The Collaborative International Dictionary of English v.0.48:

Foison \Foi"son\, n. [F. foison, fr. L. fusio a pouring,
   effusion. See Fusion.]
   Rich harvest; plenty; abundance. [Archaic] --Lowell.
   [1913 Webster]

         That from the seedness the bare fallow brings
         To teeming foison.                       --Shak.
   [1913 Webster]