The difference lies in the whisky's country of origin. American and Irish makers prefer the spelling whiskey, while Scottish and Japanese makers prefer whisky. To understand this difference, let us first look at the origin of the term whisky itself.
Whisky comes from the Gaelic word usquebaugh, itself from the Scottish Gaelic uisge beatha- which links up to the Latin aqua vitae, the water of life. Author Douglas Adams gave it a different spin in his Hitchhiker's Guide to the Galaxy. His work featured the drink Ouisghian Soda (along with Rumank Oak and Jinnan Tonyx).
From uisge beatha, the word whisky came to be, with that spelling. A distinction was born somewhere in the 1870s, when Irish distillers who were exporting to America wanted to differentiate their product from the Scottish expressions. So they started spelling their offerings with an 'e,' and thus the word whiskey was born. As Irish whiskey gained popularity in USA, American makers too started preferring the spelling whiskey.
Today, the general rule is to use the spelling as the spirit's country of origin. Thus, even an American would call it Laphroaig whisky, while a Scot would say Jameson Irish whiskey. I came across an interesting mnemonic for this here:
- Countries that have E’s in their names (UnitEd StatEs and IrEland) tend to spell it whiskEy (plural whiskeys)
- Countries without E’s in their names (Canada, Scotland, and Japan) spell it whisky (plural whiskies)
While this does cover the major malt producing nations, it can go awry with some other countries. England, for example, spells it whisky! So does it all really matter? Like it or not, yes it does. Calling it whiskEy in Scotland could get you into a lot of trouble. And I can see the Irish and Americans being equally passionate about sticking to their spelling.