The Collaborative International Dictionary of English v.0.48:

Irriguous \Ir*rig"u*ous\, a. [L. irriguus. See Irrigate.]
   [1913 Webster]
   1. Watered; watery; moist; dewy. [Obs.]
      [1913 Webster]

            The flowery lap
            Of some irriguous valley spreads her store.
                                                  --Milton.
      [1913 Webster]

   2. Gently penetrating or pervading. [Obs.] --J. Philips.
      [1913 Webster]