rain

Etymology 1

From Middle English reyn, rein, from Old English reġn, from Proto-West Germanic *regn, from Proto-Germanic *regną (compare West Frisian rein, Dutch regen, German Regen, Danish and Norwegian regn), of uncertain origin. Possibly from pre-Germanic *Hréǵ-no-, from Proto-Indo-European *Hreǵ- (“to flow”) (compare Latin rigō (“wet, soak”), Lithuanian rõki (“drizzling rain”), Albanian rrjedh (“to flow, drip”)), although the consonant reflexes don't match.

noun

1. Condensed water falling from a cloud.
   We've been having a lot of rain lately.
   The rains came late that year.
   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. (figurative) Any matter moving or falling, usually through air, and especially if liquid or otherwise figuratively identifiable with raindrops.
3. (figurative) An instance of particles or larger pieces of matter moving or falling through air.
   A rain of mortar fire fell on our trenches.

verb

1. (impersonal) To have rain fall from the sky.
   Judging by the black cloud, it will rain later today.
2. (intransitive) To fall as or like rain.
   Tears rained from her eyes.
   Leaves rained from the tree.
   Bombs rained from the sky.
3. (transitive) To issue (something) in large quantities.
   The boxer rained punches on his opponent's head.

Etymology 2

verb

1. Obsolete form of reign.