What is the longest word in English?

The longest word in English that appears in at least some dictionaries is “pneumonoultramicroscopicsilicovolcanoconiosis,” which has 45 letters. It is the name of a lung disease (pneumono) that is caused by inhaling very small (ultramicroscopic) silicone particles from a volcano. The term was coined specifically to serve as an example of a long word.

The second-longest word is “pseudopseudohypoparathyroidism” (30 letters), which is a rare genetic disorder that mimics the symptoms of a thyroid disorder.

Very long words are able to be created in English by adding prefixes and suffixes on to a base word. This process is essentially limitless, which is why most long words have several prefixes and suffixes.

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