急に雨が降り始めた。

urgent; sudden; abrupt; sharp; steep; precipitous; rapid; swift; fast; emergency; crisis; hurrying; haste; (in gagaku or noh) end of a song

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

rain

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to descend; to go down; to come down; to be handed down (of an order, judgment, etc.); to pass (of time); to surrender; to capitulate; (often in neg. form) to be less than; to be inferior to; to have the runs; to have diarrhea