Rack your brains is an idiom expression used in English as early as the 1820’s.
Meaning of Idiom ‘Rack Your Brains’
To rack one’s brains is to try very hard to remember something or figure something out. It basically means to ‘think very hard.’
The word rack can be understood to mean ‘work the brain very hard.’
Examples Of Use
“He racked his brain for hours but couldn’t remember where he had left the paperwork.”
“Christmas shopping for my wife is hard. I have to rack my brains to think of something to get her.”
Sometimes used as rack your brain.
This idiom was first recorded in 1583 as ‘rack your wits.’
From above, the word rack in this idiom means something like ‘work the brain very hard.’ But why the word rack? Rack in this context originally alluded to something more like ‘stretch’ or ‘stretch out’ as in “I stretched my brain to the breaking point!” This has a dark history as a rack was originally a tool used to stretch out a material, such as leather, but came to be used as a torture device. Rack and various related verbs in other languages came to mean ‘to stretch’ or ‘to stretch out.’
A person to be tortured was placed on the rack and his arms and legs tied and then stretched slowly and painfully by extending the rack. This torture was meant to get information out of the tortured, just as “racking your brain” is trying to get information out of your brain. So, what started as a torture to obtain information became an idiom meaning to try to remember something.
There are other archaic uses of rack, such as the expression on the rack, meaning to be in great anxiety.
There was also a variant from the same period: Cudgel one’s brains. This is the same idea but with a cudgel instead of a rack. A cudgel is a short thick stick used for beating. Shakespeare used this Hamlet (5:1): “Cudgel thy brains no more about it, for your dull ass will not mend his pace with beating.”
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