This is an extract from Wickpedia:
Names and spellings
Whisky comes from the Gaelic uisge/uisce beatha meaning "water of life", possibly modelled on the Latin phrase aqua vitae. The spelling whisky (plural whiskies) is generally used for whiskies distilled in Scotland, Wales, Canada, and Japan, while whiskey is used for the spirits distilled in Ireland. A 1968 directive of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives specifies "whisky" as the official U.S. spelling, but allows labeling as "whiskey" in deference to tradition; most U.S. producers still use the latter spelling.
A mnemonic used to remember which spelling is used is that "Ireland" and "United States" have at least one "e" in their names, while "Scotland", "Canada" and "Japan" do not. International law reserves the term "Scotch whisky" to those whiskies produced in Scotland.
Whiskies produced in other countries may not use the terms Scots, Scotch, Scotland, or Scottish. Similar conventions exist for "Irish whiskey", "Canadian whisky", and "bourbon whiskey".
In North America and parts of Continental Europe, the abbreviated term "Scotch" is usually used for "Scotch whisky". In England, Scotland, and Wales, the term "whisky" almost always refers to "Scotch whisky", and the term "Scotch" is rarely used by itself. In Welsh the forms wisgi, wysgi and chwisgi are all used. Craythur is another term for whiskey in Ireland.