Whisky... sadly NOT Kosher for Passover- it is made out of grain. For those of you new the complicated question of Kosher, here is a TON of info. Basically, Kosher is a set of dietary laws that govern food that is acceptable for Jews to eat.
Passover, the commemoration of the freedom of the Hebrews from slavery in Egypt is celebrated with long meals, lots of wine and a complete absence of leavened bread- this includes beer, and, yes, whisky.
For food to be Kosher during this 8 day festival, there is a higher standard to adherence that must be fulfilled which includes the decree that food or drink must not come in any contact with grain. Thus, food permitted for the holiday of passover will have specific labels that certify it as "Kosher for Passover."
In an incredibly impressive article on the subject of whisky and kosher, Ralph Katzenell delves into the depths of Kosher Laws, what whiskies are Kosher and even the whisky production process.
Kosher wine is a very interesting subject since wine was used for idol worshiping in the ancient times, for wine to be Kosher, a religious Jew MUST be part of the wine making process from beginning to end.
As such, many whiskies are aged in old wine or sherry barrels that, since the wine or sherry may not be kosher, preclude the whisky from being kosher. A list of Kosher whiskies can be found here.
On CelticMalts.com, we learn about the grey area of whisky being Kosher...
The grey areas of Whisky Kashrut
The [Kosher] Law frequently makes allowances for real-life difficulties, and most authorities are willing to bend a little with the wind. As noted above,Kashrut allows for accidental contamination by small quantities of non-kosher substances. And the casks are toasted, to a greater or lesser extent. Burning is a recognized procedure for rendering suspect non-kosher vessels kosher. The original concept of 'accidental' has been stretched somewhat to include what today would be recognized as 'deliberate with intent to influence the character'.