Whisk(e)y is a spirituous liquor distilled from a fermented mash of grains (barley, corn, wheat, etc.),
matured in wooden casks, usually for 2-3 years or more.
The earliest known Gaelic records refer to whisky as ‘Uisgebaugh’ and ‘Uisge Beatha’ – which in turn comes from the Latin ‘Aqua Vitae’ (‘Water of Life’).
When the very first whisk(e)y was distilled is still a matter of debate. It was probably somewhere in the 14th or 15th century – and the first distillers in Britain were most likely alchemists or monks. The actual birthplace of ‘the water of life’ was probably Ireland or Scotland.
It is mostly a matter of tradition (and there are exceptions), but as a rule of thumb, whiskies that were produced in Ireland or the United States are labeled as ‘whiskey’. The whiskies hailing from other countries are usually spelled as ‘whisky’ – without the ‘e’.
Reference source: www.maltmadness.com