The Collaborative International Dictionary of English v.0.48:

Assart \As*sart"\ ([a^]s*s[aum]rt"), n. [OF. essart the grubbing
   up of trees, fr. essarter to grub up or clear ground of
   bushes, shrubs, trees, etc., fr. LL. exartum, exartare, for
   exsaritare; L. ex + sarire, sarrire, saritum, to hoe, weed.]
   1. (Old Law) The act or offense of grubbing up trees and
      bushes, and thus destroying the thickets or coverts of a
      forest. --Spelman. --Cowell.
      [1913 Webster]

   2. A piece of land cleared of trees and bushes, and fitted
      for cultivation; a clearing. --Ash.
      [1913 Webster]

   Assart land, forest land cleared of woods and brush.
      [1913 Webster]