fat chance
idiom

- used to say that you certainly do not think that something is likely to happen

(Cambridge Advanced Learner's Dictionary)

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The word "fat" implies thick or large. One would then assume that a "fat chance" refers to a very high chance of something happening. But the English language has fooled us again. A fat chance means just the opposite and is used to indicate that someone believes there is "no chance" of something occurring. While this sounds illogical, it's easy to explain.

Like all languages, especially when spoken informally or colloquially, English contains many phrases and expressions based on humour and/or irony. This is the case with "fat chance." Consider the expression "slim chance," which as it implies means having little chance of happening. Expressing the same thought by using the opposite of slim - fat - creates a phrase that is intentionally satirical.

Folk singing legend Pete Seeger pointed out how strange English can sometimes be in his song "English is CUH-RAY-ZEE", even mentioning "slim and fat chance" in one of the verses. Here is an excerpt from the song, which is actually spoken more than sung:

Why is it that night falls but never breaks and day breaks but never falls?
In what other language do people drive on the parkway and park on the driveway?
Ship by truck but send cargo by ship? Recite at a play but play at a recital?
Have noses that run and feet that smell?
English is cuh-ray-zee!

How can a slim chance and a fat chance be the same
When a wise man and a wise guy are very different?
To overlook something and to oversee something are very different,
But quite a lot and quite a few are the same.
How can the weather be hot as hell one day and cold as hell the next?
English is cuh-ray-zee!

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SYNONYMS

no chance in hell, a snowball's chance in hell, when hell freezes over, not a ghost of a chance, a chance in a million

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Practice OWAD into today's conversation, say something like

"In this traffic, there's FAT CHANCE that we'll be on time for the meeting, let's call in from the road."