Longest word in a major English dictionary

What to remember

At 45 letters, pneumonoultramicroscopicsilicovolcanoconiosis is the longest word found in any of the major English language dictionaries.

Naming the longest word in English is not simple: it depends on what counts as a word and how length is measured. Place names may or may not count, technical terms can be stretched at will, and adding prefixes and suffixes produces grammatically correct words that nobody uses. Each dictionary includes and leaves out different words.

Most often, length means the number of written letters. It can also be measured in spoken sounds, or phonemes, though that approach is less common.