Why is exhaust manifold called a manifold?

The word "manifold" comes from the Old English adjective monigfald, which basically means "many-fold".

At some point in the 19th century, the term became a noun describing "a pipe with several outlets", and has since become a common mechanical engineering term for such components.

The same term was also used to describe manifold geometry.

So both senses of the meaning branch from the original adjective "many-fold", rather than stemming from each other directly.

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