1715, from Gaelic uisge beatha "whisky," literally "water of life," from Old Irish uisce "water" (from PIE *ud-skio-, suffixed form of root *wed- (1) "water; wet") + bethu "life" (from PIE *gwi-wo-tut-, suffixed form of *gwi-wo-, from root *gwei- "to live").
According to Barnhart, the Gaelic is probably a loan-translation of Medieval Latin aqua vitae, which had been applied to intoxicating drinks since early 14c. (compare French eau de vie "brandy"). Other early spellings in English include usquebea (1706) and iskie bae (1580s). In Ireland and Scotland obtained from malt; in the U.S. commonly made from corn or rye. Spelling distinction between Scotch whisky and Irish and American whiskey is a 19c. innovation. Whisky sour is recorded from 1889.