The Collaborative International Dictionary of English v.0.48:

Viridity \Vi*rid"i*ty\, n. [L. viriditas, fr. viridis green: cf.
   F. viridit['e]. See Verdant.]
   1. Greenness; verdure; the color of grass and foliage.
      [1913 Webster]

   2. Freshness; soundness. [Obs.] --Evelyn.
      [1913 Webster]

WordNet (r) 3.0 (2006):

viridity
    n 1: green color or pigment; resembling the color of growing
         grass [syn: green, greenness, viridity]