Silent vāv

The Silent vāv is an element of Persian and Urdu orthography resulting when a vāv is preceded by khe and often followed by an alef or ye, forming the combination of خوا or خوی, in which the vāv is silenced. It is always written but not typically spoken, except for in certain eastern Persian dialects wherein it is pronounced. If not followed by a long vowel, the vāv following a khe sometimes adopts the sound of the short vowel zamme/pish. It was also formerly made use of when dealing with Persian loanwords in the Arabic scripts of Turkic languages, particularly in Ottoman Turkish.

Historical development
The silent vāv occurs only in words of Iranian origin, and is not present in any Turkic or Arabic loanwords that entered the language. Words in Middle Persian containing the labialised voiceless velar fricative preceding a long vowel developed such that the sound underwent delabialization and simply became the voiceless velar fricative. In cases where it preceded the short near-open front unrounded vowel it delabialised and took on the sound of the close-mid back rounded vowel, evolving from  to. Despite this, the written language continues to reflect the old standards of pronunciation, hence the silent vāv remains written. These linguistic evolutions did not take place in certain areas of Greater Iran, and thus certain dialects do not have the silent vāv as a feature.

In poetry
Historically, sometimes poetic usages of the silent vāv did not follow the traditional literary rules and guidelines. This can be seen in the following poem by Sa'adi in his Bustan book: Phonetic transcription:    According to the Persian literary rules, خود should be pronounced as ; however, as is visible in this poem, it atypically takes on the sound of  and rhymes with بد/ in the verse following it. This silent vāv taking on the sound of fathe/zebar,, rather than the of zamme/pish, is a very common feature in classical Persian poetry, also seen, for example, in the works of Ferdowsi and Nezami.

Geographical distribution.
The standard Iranian form of Persian, does not pronounce the silent vāv in any situation. Tajiki Persian, which has undergone delabialisation in the same way as Iranian Persian, is written in the Cyrillic script, and thus does not have the silent vāv as an orthographic feature. However, the Afghan dialects of Persian, commonly known as Dari, as well as the Persian dialects of Kashan and some other regions of Iran, continue to pronounce the vāv, meaning that the silent vāv is not a feature of the orthography of their dialects. In Urdu, labialisation is retained in some words and not others. In some words, the and  pronunciation variants are interchangeable.