The Collaborative International Dictionary of English v.0.48:

Vert \Vert\, n. [F., green, from L. viridis. See Verdant, and
   cf. Verd.]
   1. (Eng. Forest Law)
      (a) Everything that grows, and bears a green leaf, within
          the forest; as, to preserve vert and venison is the
          duty of the verderer.
      (b) The right or privilege of cutting growing wood.
          [1913 Webster]

   2. (Her.) The color green, represented in a drawing or
      engraving by parallel lines sloping downward toward the
      right.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

VERT. Everything bearing green leaves in a forest. Bac. Ab. Courts of the
Foreat; Manwood, 146.