Lewis & Short

rōrātĭo, ōnis, f. [roro], a falling of dew, dew.

  1. I. Lit., Vitr. 8, 2, 2.
    In plur.: nocturnae, App. M. 9, p. 232, 6.
  2. II. Transf.
    1. A. The falling off of the grape in consequence of a cold dew (a disease of the grapes), Plin. 17, 24, 37, § 226.
    2. B. A dropping in the clepsydra, Cassiod. Var. 1, 48.