Definition of "rain"

rain¹

/ɹeɪn/

noun
usually uncountable, plural rains
1. Condensed water falling from a cloud.
  Quotations
  This process involves cloud seeding – when various substances are put into clouds in an attempt to cause rain. Audio (US)(file)
  2019, VOA Learning English (public domain)
2. (figuratively) Any matter moving or falling, usually through air, and especially if liquid or otherwise figuratively identifiable with raindrops.
3. (figuratively) An instance of particles or larger pieces of matter moving or falling through air.
verb
third-person singular simple present rains, present participle raining, simple past and past participle rained
1. (impersonal) To have rain fall from the sky.
2. (intransitive) To fall as or like rain.
  Quotations
  The rain it raineth every day.
  c. 1601–1602 (date written), William Shakespeare, “Twelfe Night, or What You Will”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act V, scene i]
3. (transitive) To issue (something) in large quantities.

rain²

/ɹeɪn/

verb
third-person singular simple present rains, present participle raining, simple past and past participle rained
1. Obsolete form of reign.
  Quotations
  Such wondrous science in mans witt to rain.
  1590, Edmund Spenser, “Book I, Canto V”, in The Faerie Queene. […], London: […] [John Wolfe] for William Ponsonbie