rain (Noun) — Water falling in drops from vapour condensed in the atmosphere. ex. "the mean annual rain"
rain (Noun) — Drops of fresh water that fall as precipitation from clouds.
rain (Noun) — Anything happening rapidly or in quick succession. ex. "a rain of bullets"
rain (Verb) — Precipitate as rain. ex. "If it rains much more, we can expect some flooding"
rain (Verb) — Fall or cause to fall in large quantities.