In phonology, syncope (; from Ancient Greek: ?, romanized: sunkop?, lit. 'cutting up') is the loss of one or more sounds from the interior of a word, especially the loss of an unstressed vowel. It is found both in synchronic analysis of languages and diachronics. Its opposite, whereby sounds are added, is epenthesis.
Synchronic analysis studies linguistic phenomena at one moment of a language's history, usually the present. In modern languages, syncope occurs in inflection, poetry, and informal speech.
In languages such as Irish, the process of inflection can cause syncope:
- imir (to play) should become *imirím (I play). However, the addition of the -ím causes syncope and the second-last syllable vowel i is lost so imirim becomes imrím.
- inis (island) should become *inise in the genitive case. However, instead of *Baile na hInise, road signs say, Baile na hInse (the town of the island). Once again, there is the loss of the second i.
If the present root form in Irish is the result of diachronic syncope, synchronic syncope for inflection is prevented.
As a poetic device
Sounds may be removed from the interior of a word as a rhetorical or poetic device: for embellishment or for the sake of the meter.
- Latin comm?verat > poetic comm?rat ("he had moved")
- English hastening > poetic hast'ning
- English heaven > poetic heav'n
- English over > poetic o'er
- English ever > poetic e'er, often confused with ere ("before")
Various sorts of colloquial reductions might be called "syncope" or "compression".
Contractions in English such as "didn't" or "can't" are typically cases of syncope.
- English Australian > colloquial Strine, pronounced
- English did not > didn't, pronounced
- English I would have > I'd've, pronounced
- English going to > colloquial gonna (generally only when unstressed and when expressing intention rather than direction), pronounced or, before a vowel,
- English every pronounced ['?v?i]
- English library pronounced as 
In historical phonology, the term "syncope" is often limited to the loss of an unstressed vowel, in effect collapsing the syllable that contained it: trisyllabic Latin calidus (stress on first syllable) develops as bisyllabic caldo in several Romance languages.
Loss of any sound
Loss of unstressed vowel
A syncope rule has been identified in Tonkawa, an extinct American Indian language in which the second vowel of a word was deleted unless it was adjacent to a consonant cluster or a final consonant.