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noun

cosh

KOSH

Cosh (noun) means a short, heavy stick or weighted tube used as a weapon to strike someone, especially over the head. Example: “The robber carried a leather cosh weighted with lead shot.”

noun
1
British A short, heavy stick or weighted tube used as a weapon to strike someone, especially over the head.
"The robber carried a leather cosh weighted with lead shot."
"Police recovered a cosh from the boot of the car."
2
mathematics The hyperbolic cosine function, written cosh x, defined as half the sum of e to the x and e to the minus x.
"A hanging chain takes the shape of a curve described by cosh."
verb
1
British To hit someone with a cosh or other heavy object.
"He was coshed from behind and left in the alley."

How to Use Cosh

Learner’s notes

In plain EnglishA short heavy stick used to hit someone; in maths, the hyperbolic cosine.

When to use it

The weapon sense is chiefly British and somewhat old-fashioned, common in crime writing. The maths sense is fully technical and international.

Memory tip

In maths, cosh pairs with sinh and tanh — the h stands for hyperbolic.

Easily confused with
Common pairings
under the cosh coshed over the head leather cosh cosh and sinh
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The robber carried a leather _____ weighted with lead shot.

Related Words

Rhymes for cosh

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Frequently Asked Questions

What is the difference between a cosh and a truncheon?

A truncheon is a rigid baton issued to police as standard equipment, while a cosh is typically shorter, often flexible or weighted at one end, and is associated with improvised or criminal use. In many jurisdictions carrying a cosh is an offence in itself.

How do you pronounce cosh in maths?

Most mathematicians say it as a single syllable, 'kosh', rhyming with 'posh'. Some read it aloud as 'cos-h' or 'hyperbolic cosine', particularly when clarity matters.

What does 'under the cosh' mean?

It is a British idiom meaning under heavy pressure or sustained attack, used especially in sport and business. A team defending desperately for the last twenty minutes is said to be under the cosh.

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