cooler
n.— «To win a multi-day tournament, a player must be able to overcome the inevitable bad beat or “cooler,” which is defined as a great hand that just runs into a better hand (for example K-K vs. A-A). The way players respond to this bit of bad luck can determine whether they survive in the event or get sent to the rail.» —“’Cooler’ head prevails at Foxwoods” by Bernard Lee Boston Herald (Massachusetts) Mar. 2, 2008. (source: Double-Tongued Dictionary)
Further reading
In 1968, students at Cheyenne High School in Cheyenne, Wyoming, compiled a collection of their own slang, including the word Clyde, used to refer to one’s head, as in Use your Clyde! This is part of a complete episode.
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The author of this article implies, incorrectly, that a bad beat and a cooler are the same thing. They’re quite different.
A cooler is when you’re dealt an exceptionally good hand, that happens to be in second place. An example would be having KK v TT on a KTT flop. You just can’t help but put all your money in the middle, even though you’re losing.
A bad beat is when you are ahead (statistically) when the money goes in, but then your opponent catches a lucky card or combination of cards to win. An example of a bad beat would be if you had AJ versus TT on an AAJ flop, TT bluff-raises all-in, you call ng tens to win.