A wee bit of research ... Maclean's Miscellany of Whisky .. does wonders. It shows that the words whisky and whiskey were quite interchangable until recently when, possible blind drunk 'people' wanted to believe that one word meant Scottish and the other Irish and/or Scotch could only mean drink and not an adjective for other things unless it excluded people. If you are a serious whisk(e)y drinker you'll know that the best way to get the flavour is always to add a little water.
Slainte.