That word is 'blend,' as in 'blended whiskey.' The rules say a combination of two or more different whiskeys is a blend, but a combination of two or more whiskeys that have the same classification is not a blend. Therefore Four Roses Yellow Label (pictured, above) is labeled 'Kentucky Straight Bourbon Whiskey,' even though it is a blend of ten different straight bourbons.
'Blend' is generally considered a dirty word because it can also mean a combination of straight whiskey with neutral spirits (i.e., vodka). In the USA and nowhere else, a mixture that is 80 percent vodka and just 20 percent whiskey can be called 'blended whiskey.' Since that describes most blends on the market, it's no wonder the word is eschewed.
Then there is Four Roses Yellow Label. A perfectly good way to describe this product is as a blend of ten different bourbon recipes. They usually resort to 'mixture' or 'combination' to avoid the dreaded b-word.
Four Roses arrives at ten recipes by combining two different mash bills with five different yeasts. They explain it all very well on their web site, here. Although Four Roses likes to talk about the ten recipes and the characteristics of their five yeasts, what they won't tell you are the all-important proportions. How much OBSK is in yellow label, how much OESO.
Four Roses used to be owned by Seagrams and blending is very Seagramsey. Crown Royal, the best-selling of what used to be Seagrams whiskeys, is a Canadian Blended Whisky. Canadian rules are very different and Canadian blends are respectable, as are Scotch blends. It's only a dirty word here.
This is too bad, because as the American whiskey industry continues to evolve, blending has a lot of potential. Wild Turkey has just released a limited edition called Forgiven that blends straight bourbon with straight rye. They say it was an accident but it looks more like a deliberate imitation of High West's Bourye. Jim Beam's Devil's Cut could be considered an all-bourbon blend since it combines regular Jim Beam Bourbon with the very smoky bourbon they extract from empty barrels. The 2012 edition of Heaven Hill's Parker's Heritage Collection (PHC) combined rye-recipe bourbon with wheated bourbon.
Four Roses Yellow Label is an excellent bourbon and a great value at around $20, but the 2012 PHC really shows the potential of all-whiskey blends. It is an example of what whiskey-makers at the height of their powers can accomplish. The whiskeys selected and the blending proportions (never revealed) resulted in a superb whiskey that is so much more than the sum of its parts, it ranks as one of the best American whiskeys ever made.
With micro-distillers inventing new whiskeys every day, and with MGP of Indiana making more than ten different whiskey recipes, blending is becoming a way for non-distiller producers (NDPs) to create original whiskeys rather than just bottling an existing whiskey made by one of the major distilleries. That's revolutionary and could be really cool, especially if the NDPs don't lie about it (a long shot).