Metathesis (mɪˈtæθɪsɪs; from Greek μετάθεσις, from μετατίθημι "I put in a different order"; Latin: transpositio) is the transposition of sounds or syllables in a word or of words in a sentence. Most commonly, it refers to the interchange of two or more contiguous segments or syllables, known as adjacent metathesis or local metathesis:
foliage > **foilage (adjacent segments)
anemone > **anenome (adjacent syllables)
cavalry > **calvary (codas of adjacent syllables)
Metathesis may also involve interchanging non-contiguous sounds, known as nonadjacent metathesis, long-distance metathesis, or hyperthesis, as shown in these examples of metathesis sound change from Latin to Spanish:
Latin parabola > Spanish palabra "word"
Latin miraculum > Spanish milagro "miracle"
Latin periculum > Spanish peligro "danger, peril"
Latin crocodilus > Spanish cocodrilo "crocodile"
Many languages have words that show this phenomenon, and some even use it as a regular part of their grammar, such as Hebrew and Fur. The process of metathesis has altered the shape of many familiar words in English as well.
The original form before metathesis may be deduced from older forms of words in the language's lexicon or, if no forms are preserved, from phonological reconstruction. In some cases it is not possible to settle with certainty on the original version.
Dionysius of Halicarnassus was a historian and scholar in rhetoric living in 1st century BC Greece. He analysed classical texts and applied several revisions to make them sound more eloquent. One of the methods he used was re-writing documents on a mainly grammatical level: changing word and sentence orders would make texts more fluent and "natural", he suggested. He called this way of re-writing metathesis.
In ASL, several signs which have a pre-specified initial and final location (such as the signs RESTAURANT, PARENT, TWINS) can have the order of these two locations reversed in contexts which seem to be purely phonological. While not possible with all signs, this does happen with quite a few.