Qoph
Qoph is the nineteenth letter of the Semitic abjads, including Phoenician qōp , Hebrew qūp̄ ק, Aramaic qop , Syriac qōp̄ ܩ, and Arabic qāf ق.
Its original sound value was a West Semitic emphatic stop, presumably [kʼ]. In Hebrew numerals, it has the numerical value of 100.

Origins
The origin of the glyph shape of qōp () is uncertain. It is usually suggested to have originally depicted either a sewing needle, specifically the eye of a needle (Hebrew קוף quf and Aramaic קופא qopɑʔ both refer to the eye of a needle), or the back of a head and neck (qāf in Arabic meant "nape").
According to an older suggestion, it may also have been a picture of a monkey and its tail (the Hebrew קוף means "monkey").Besides Aramaic Qop, which gave rise to the letter in the Semitic abjads used in classical antiquity, 
Phoenician  qōp is also the origin of the Latin letter Q and Greek Ϙ (qoppa) and Φ (phi).

Hebrew Qof
The Oxford Hebrew-English Dictionary transliterates the letter Qoph (קוֹף‎) as q or k; and, when word-final, it may be transliterated as ck. 
The English spellings of Biblical names (as derived via Latin from Biblical Greek) containing this letter may represent it as c or k, e.g. Cain for Hebrew Qayin, or Kenan for Qenan (Genesis 4:1, 5:9).

Pronunciation
In modern Israeli Hebrew the letter is also called kuf. The letter represents /k/; i.e., no distinction is made between the pronunciations of Qof and Kaph (in modern Hebrew).
However, many historical groups have made that distinction, with Qof being pronounced [q] by Iraqi Jews and other Mizrahim, or even as [ɡ] by Yemenite Jews under the influence of Yemeni Arabic.
Qoph is consistently transliterated into classical Greek with the unaspirated〈κ〉/k/, while Kaph (both its allophones) is transliterated with the aspirated〈χ〉/kʰ/. Thus Qoph was unaspirated /k/ where Kaph was /kʰ/, this distinction is no longer present. Further we know that Qoph is one of the emphatic consonants through comparison with other Semitic languages, and most likely was ejective /kʼ/. In Arabic the emphatics are pharyngealised and this causes a preference for back vowels, this is not shown in Hebrew orthography. Though the gutturals show a preference for certain vowels, Hebrew emphatics do not in Tiberian Hebrew (the Hebrew dialect recorded with vowels) and therefore were most likely not pharyngealised, but ejective,  pharyngealisation being a result of Arabisation.

Numeral
Qof in Hebrew numerals represents the number 100. Sarah is described in Genesis Rabba as בת ק' כבת כ' שנה לחטא‎, literally "At Qof years of age, she was like Kaph years of age in sin", meaning that when she was 100 years old, she was as sinless as when she was 20.

Arabic Qāf
The Arabic letter ق is named قاف qāf. It is written in several ways depending in its position in the word:

Traditionally in the scripts of the Maghreb it is written with a single dot, similarly to how the letter fā ف is written in Mashreqi scripts:
It is usually transliterated into Latin script as q, though some scholarly works use ḳ.

Pronunciation
According to Sibawayh, author of the first book on Arabic grammar, the letter is pronounced voiced (maǧhūr), although some scholars argue, that Sibawayh's term maǧhūr implies lack of aspiration rather than voice. As noted above, Modern Standard Arabic has the voiceless uvular plosive /q/ as its standard pronunciation of the letter, but dialectical pronunciations vary as follows:
The three main pronunciations:

[q]: in most of Tunisia, Algeria and Morocco, Southern and Western Yemen and parts of Oman, Northern Iraq, parts of the Levant (especially the Alawite and Druze dialects). In fact, it is so characteristic of the Alawites and the Druze that Levantines invented a verb "yqaqi" /jqæqi/ that means "speaking with a /q/". However, most other dialects of Arabic will use this pronunciation in learned words that are borrowed from Standard Arabic into the respective dialect or when Arabs speak Modern Standard Arabic.
[ɡ]: in most of the Arabian Peninsula, Northern and Eastern Yemen and parts of Oman, Southern Iraq, some parts within Jordan, eastern Syria and southern Palestine, Upper Egypt (Ṣaʿīd), Sudan, Libya, Mauritania and to lesser extent in some parts of Tunisia, Algeria, and Morocco but it is also used partially across those countries in some words.
[ʔ]: in most of the Levant and Egypt, as well as some North African towns such as Tlemcen and Fez.Other pronunciations:

[ɢ]: In Sudanese and some forms of Yemeni, even in loanwords from Modern Standard Arabic or when speaking Modern Standard Arabic.
[k]: In rural Palestinian it is often pronounced as a voiceless velar plosive [k], even in loanwords from Modern Standard Arabic or when speaking Modern Standard Arabic.Marginal pronunciations:

[d͡z]: In some positions in Najdi, though this pronunciation is fading in favor of [ɡ].
[d͡ʒ]: Optionally in Iraqi and in Gulf Arabic, it is sometimes pronounced as a voiced postalveolar affricate [d͡ʒ], even in loanwords from Modern Standard Arabic or when speaking Modern Standard Arabic.
[ɣ] ~ [ʁ]: in Sudanese and some Yemeni dialects (Yafi'i), and sometimes in Gulf Arabic by Persian influence, even in loanwords from Modern Standard Arabic or when speaking Modern Standard Arabic.

Velar Gāf
It is not well known when the pronunciation of Qāf ⟨ق⟩ as a velar [ɡ] occurred or the probability of it being connected to the pronunciation of Jīm ⟨ج⟩ as an affricate [d͡ʒ], but the Arabian peninsula which is the homeland of the Arabic language, there are two sets of pronunciations, either the ⟨ج⟩ represents a [d͡ʒ] and ⟨ق⟩ represents a [ɡ] which is the main pronunciation in  most of the peninsula except for western and southern Yemen and parts of Oman where ⟨ج⟩ represents a [ɡ] and ⟨ق⟩ represents a [q]. 
The Standard Arabic (MSA) combination of ⟨ج⟩ as a [d͡ʒ] and ⟨ق⟩ as a [q] does not occur in any natural modern dialect in the Arabian peninsula, which shows a strong correlation between the palatalization of ⟨ج⟩ to [d͡ʒ] and the pronunciation of the ⟨ق⟩ as a [ɡ] as shown in the table below:

Notes:

Western and southern Yemen:  Taʽizzi-Adeni and Tihamiyya dialects (coastal Yemen), in addition to southwestern (Salalah region) and eastern Oman, including Muscat, the capital.
[ʒ] is an allophone in eastern Arabia.
Actually, the [d͡ʒ] variant is the preferred pronunciation when taught outside of Arabic speaking countries where the local variant of ج is accepted as the standard, namely [d͡ʒ], [ʒ], [ɟ], or [ɡ].
In Sanaa, [ɡ] is used as the literary standard for ق, whereas the literary standard pronunciation in Sudan is [ɢ] or [ɡ].

Maghrebi variant
The Maghrebi style of writing qāf is different: having only a single point (dot) above; when the letter is isolated or word-final, it may sometimes become unpointed.
The earliest Arabic manuscripts show qāf in several variants: pointed (above or below) or unpointed. Then the prevalent convention was having a point above for qāf and a point below for fāʼ; this practice is now only preserved in manuscripts from the Maghribi, with the exception of Libya and Algeria, where the Mashriqi form (two dots above: ق) prevails.
Within Maghribi texts, there is no possibility of confusing it with the letter fāʼ, as it is instead written with a dot underneath (ڢ‎) in the Maghribi script.

Unicode
References


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