Medireview was an accidental non-word for medieval, created in 2001 as the result of an issue with Yahoo!'s email service.

In 2001 Yahoo! silently introduced an email filter which changed some strings in HTML emails considered to be dangerous. While it was intended to stop spreading JavaScript viruses, no attempts were made to limit these string replacements to script sections and attributes, out of fear this would leave some loophole open. Additionally, word boundaries were not respected in the replacement.

The list of replacements:

An unintended side-effect of this was the change of medieval to medireview. Unfortunately not all email recipients recognised this as an error or may have even thought it was a recent innovation. As of 2007 there are still web pages seen which use medireview instead of medieval. Among other effects were the replacement of evaluation with reviewuation, expressionist with statementist, and the replacement of the French word cheval (horse) with chreview.

Medireview has been referred to as a neologism (an invented word), but it was not invented and it is not, by definition, a word. It has no meaning and is the equivalent of a computer typo (compare with teh, a common human typo for the, which has become part of internet slang).

While individuals promoting their neologisms on the internet is quite common, the medireview case is the best known of some rare cases where this happened by accident.