Rain n. & v. : Reign.

Rain n. : Water falling in drops from the clouds; the descent of water from the clouds in drops.

Rain n. : To fall in drops from the clouds, as water; -- used mostly with it for a nominative; as, it rains.

Rain n. : To fall or drop like water from the clouds; as, tears rained from their eyes.

Rain v. t. : To pour or shower down from above, like rain from the clouds.

Rain v. t. : To bestow in a profuse or abundant manner; as, to rain favors upon a person.

Example:
What is the difference between Rain showers and Rain?

Taxonomy
rain, raindrops, precipitation, precipitation rate, Cherrapunji, weather, 2006-10-19, search, heavy rain, Chocó, Earth & Sky, free encyclopedia, acid rain, Tutunendo, Averages, 04-07, 12-11, Australian Government.

Defination from the web:
Rain is the primary source of fresh water for most areas of the world, providing suitable conditions for diverse ecosystems, as well as water for ... numerous protection devices such as umbrellas and raincoats, and diversion devices such as gutters and storm drains that lead rains to sewers. ...