In some Semitic languages, such as Arabic, nunation (Arabic: تنوين tanwīn) is the addition of a final nūn sound to a noun or adjective to indicate that it is fully declinable and syntactically unmarked for definiteness.
There are three of these vowel diacritics, and the signs indicate, from left to right, the endings -un (nominative case), -in (genitive), and -an (accusative). The sign ـً is most commonly written in combination with ا alif (ـًا), ةً (tāʾ marbūṭa تاء مربوطة) or stand-alone ءً (hamza همزة). An alif should always be written unless the word ends in tāʾ marbūṭa or hamza or is a diptote, even though the -un, -an or -in is not written.
Since Arabic has no indefinite article, nouns in a syntactic context unmarked for definiteness are generally indefinite; this has led to the extremely common but inaccurate belief that nunation is a marker for indefiniteness and is analogous to an indefinite article. The lack of a marker for definiteness does not necessarily make a word indefinite; in fact, many definite nouns (proper names) take nunation, as for example in the expression أشهد أن محمدًا رسول الله (ašhadu anna muḥammadan rasūlu allāh: "I witness that Muhammad is the messenger of God."), in which the name Muḥammad, a definite noun, is nunated.
Nunation may also refer to the -n ending of duals in Akkadian (until it was dropped in the Old Babylonian period).