Old English scur "a short fall of rain, storm, tempest; fall of missiles or blows; struggle, commotion; breeze," from Proto-Germanic *skuraz (source also of Old Norse skur, Old Saxon and Old Frisian scur "fit of illness;" Old High German scur, German Schauer "shower, downpour;" Gothic skura, in skura windis "windstorm"), from PIE root *kew-(e)ro- "north, north wind" (source also of Latin caurus "northwest wind;" Old Church Slavonic severu "north, north wind;" Lithuanian šiaurus "raging, stormy," šiaurys "north wind," šiaurė "north").
Of blood, tears, etc., from c. 1400. Of meteors from 1835. Sense of "bath in which water is poured from above" first recorded 1851 (short for shower-bath, itself attested from 1803). Meaning "large number of gifts bestowed on a bride" (1904, American English colloquial) later was extended to the party at which it happens (1926). Shower curtain attested from 1914.