Nunation

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.