respelling of Old English hw- attested from 11c., but not the common form until after c. 1400. It represents PIE *kw-; in German reduced to simple w-, in Scandinavian as hv-, kv-, or v-.
It also was added unetymologically to some borrowed words (whisk, whiskey) and some native words formerly spelled with simple w- or h- (whole, whore). In the 15c. flowering of its use it also threatened to change the spelling of hot, home and many more. In northern English 16c.-18c., sometimes altered to quh- (see Q). Proper pronunciation has been much in dispute in educated speech.
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.