R

R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ar (pronounced /ˈɑːr/ ^ⓘ), plural ars.

The letter ⟨r⟩ is the eighth most common letter in English and the fourth-most common consonant, after ⟨t⟩, ⟨n⟩, and ⟨s⟩.

The name of the letter in Latin was er (/ɛr/), following the pattern of other letters representing continuants, such as ⟨F⟩, ⟨L⟩, ⟨M⟩, ⟨N⟩, and ⟨S⟩. This name is preserved in French and many other languages. In Middle English, the name of the letter changed from /ɛr/ to /ar/, following a pattern exhibited in many other words such as farm (compare French ferme) and star (compare German Stern).

In Hiberno-English, the letter is called /ɒr/ or /ɔːr/, somewhat similar to oar, ore, orr.

The letter ⟨R⟩ is sometimes referred to as the littera canīna 'canine letter', often rendered in English as the dog's letter. This Latin term referred to the Latin ⟨R⟩ that was trilled to sound like a growling dog, a spoken style referred to as vōx canīna 'dog voice' (e.g. in Spanish perro 'dog').

The letter ⟨R⟩ is believed to derive ultimately from an image of a head, used in Semitic alphabets for the sound /r/ because the word for 'head' was rêš or similar in most Semitic languages. The word became the name of the letter, as an example of acrophony.

It developed into Greek ⟨Ρ⟩ ῥῶ (rhô) and Latin ⟨R⟩. The descending diagonal stroke develops as a graphic variant in some Western Greek alphabets (writing rho as ⟨⟩), but it was not adopted in most Old Italic alphabets; most Old Italic alphabets show variants of their rho between a ⟨P⟩ and a ⟨D⟩ shape, but without the Western Greek descending stroke. Indeed, the oldest known forms of the Latin alphabet itself of the 7th to 6th centuries BC, in the Duenos and the Forum inscription, still write ⟨r⟩ using the ⟨P⟩ shape of the letter. The Lapis Satricanus inscription shows the form of the Latin alphabet around 500 BC. Here, the rounded, closing ⟨Π⟩ shape of the ⟨p⟩ and the ⟨Ρ⟩ shape of the ⟨r⟩ have become difficult to distinguish. The descending stroke of the Latin letter ⟨R⟩ has fully developed by the 3rd century BC, as seen in the Tomb of the Scipios sarcophagus inscriptions of that era. From c. 50 AD, the letter ⟨P⟩ would be written with its loop fully closed, assuming the shape formerly taken by ⟨R⟩.

The minuscule form ⟨r⟩ developed through several variations on the capital form. Along with Latin minuscule writing in general, it developed ultimately from Roman cursive via the uncial script of Late Antiquity into the Carolingian minuscule of the 9th century.