The Collaborative International Dictionary of English v.0.48:

Rain \Rain\, v. i. [imp. & p. p. Rained (r[=a]nd); p. pr. &
   vb. n. Raining.] [AS. regnian, akin to G. regnen, Goth.
   rignjan. See Rain, n.]
   1. To fall in drops from the clouds, as water; -- used mostly
      with it for a nominative; as, it rains.
      [1913 Webster]

            The rain it raineth every day.        --Shak.
      [1913 Webster]

   2. To fall or drop like water from the clouds; as, tears
      rained from their eyes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

raining
    adj 1: falling in drops or as if falling like rain; "watched the
           raining apple blossoms"