Do you remember? 
Do you remember when you were a child, learning (then gleefully reciting) what you thought was the longest word in the English language? Was it ANTI­DIS­ESTABLISH­MENT­ARIAN­ISM? Or the similarly long SUPER­CALI­FRAGI­LISTIC­EXPI­ALI­DOCIOUS? There are longer ones...

However, there is no easy answer that we can give when our visitors ask us for the longest word in the English language. Most very long words only occur in one or two dictionaries, and often they are debatably not words at all. For example, ANTI­DIS­ESTABLISH­MENT­ARIAN­ISM has possibly never really been used to mean "the belief which opposes removing the tie between church and state." Certainly 99 in 100 times it is used as an example of a long word. And who says you can't put NON– (for example) on the beginning to make it even longer?

This problem is even more evident in chemical names. Most chemicals are named using a systematic naming system which methodically describes the molecule's structure. Some molecules, such as proteins, are huge, so it is possible to come up with genuine words containing millions of letters. But of course no chemist uses these really long names in practice.

Here we look at some of the longest words in English dictionaries, and discuss whether they should be considered to be real words. Interesting long chemical terms and place names are listed separately afterwards. The red numbers indicate the length (number of letters) of the word that follows.