From Wikipedia:
Legal definition
Key regulations defining Irish whiskey and its production are established by the Irish Whiskey Act of 1980,[7] and are relatively simple (for example, in contrast with those for Scotch and Bourbon whiskey). They can be summarised as follows:
Irish whiskey must be distilled and aged on the island of Ireland; that is, either in the Republic of Ireland or Northern Ireland
The contained spirits must be distilled to an alcohol by volume level of less than 94.8% from a yeast-fermented mash of cereal grains (saccharified by the diastase of malt contained therein, with or without other natural diastases) in such a way that the distillate has an aroma and flavour derived from the materials used
The product must be aged for at least three years in wooden casks of a capacity not exceeding 700 litres (185 US gal; 154 imp gal)
If the spirits comprise a blend of two or more such distillates, the product is referred to as a "blended" Irish whiskey
There are several types of whiskey common to Ireland, including those referred to as "single pot still", "single malt", "single grain", and "blended". But in contrast to the Scotch Whisky Regulations of 2009, the Irish Whiskey Act of 1980 does not actually contain a definition of the terms "single malt Irish whiskey" or "single grain Irish whiskey" or specific rules governing their production, so the exact definitions of these terms may not be clearly established.
And then there's...
http://mentalfloss.com/article/30278/what’s-difference-between-scotch-whiskey-and-bourbon
What makes a whiskey bourbon?
The law. While knocking back a dram of bourbon is a decidedly carefree exercise, making it is exceedingly technical and requires that the whiskey meet a rigid set of criteria. The Federal Standards of Identity for Bourbon stipulate what is and what isn’t bourbon. For a whiskey to call itself bourbon, its mash, the mixture of grains from which the product is distilled, must contain at least 51% corn. (The rest of the mash is usually filled out with malted barley and either rye or wheat.) The mash must be distilled at 160 proof or less, put into the barrel at 125 proof or less, and it must not contain any additives. The distillate must be aged in a new charred oak barrel. (Most often these barrels are white oak, but they can be any variety of oak.) If you distill a whiskey in your kitchen that meets all of these standards, congrats, you’ve made bourbon. Also, you’ve broken the law; the ATF is probably outside your house right now.
The main difference between scotch and whisky is geographic, but also ingredients and spellings. Scotch is whisky made in Scotland, while bourbon is whiskey made in the U.S.A, generally Kentucky. Scotch is made mostly from malted barley, while bourbon is distilled from corn. If you’re in England and ask for a whisky, you’ll get Scotch. But in Ireland, you’ll get Irish whiskey (yep, they spell it differently for a little colour).
On this side of the pond, we have our own local color, too. The difference between Tennessee Whiskey, like Jack Daniel’s, for example, and Bourbon is that after the spirit is distilled, Tennessee Whiskey is filtered through sugar-maple charcoal. This filtering, known as the Lincoln County Process, is what distinguishes Tennessee Whiskey from your average Bourbon, like Jim Beam. The name, Bourbon, comes from an area known as Old Bourbon, around what is now Bourbon County, Kentucky.
On top of these types of whiskey, we also have Rye, which can refer either to American rye whiskey, which must be distilled from at least 51 percent rye or Canadian whisky, which may or may not actually include any rye in its production process. Confusing! Right?
= new reply since forum marked as read
) Until now I had thought that all cheap Scotch was Clan MacGregor! 
-- while I was laid up with a broken ankle. 
