eighteenth letter of the English alphabet, traceable to Phoenician and always representing more or less the same sound, which in many languages is typically so resonant and continuous as to be nearly akin to the vowels, but in English is closer to -l-.

It was aspirated at the start of words (hr-) in Old English, as in Greek, but this was abandoned in English spelling and pronunciation by the end of the Old English period, but the rh- spelling survives in many words borrowed from Greek. In many languages and some dialects (e.g. Scottish) it is pronounced with a distinct trilling vibration of the tongue-tip, which gave it its ancient nickname of "the dog letter;" in other regional dialects (e.g. Boston) it is omitted unless followed by a vowel, while in others it is introduced artificially in pronunciation ("idear," "drawring," tomorrer for tomorrow is attested in print by 1901).

If all our r's that are written are pronounced, the sound is more common than any other in English utterance (over seven per cent.); the instances of occurrence before a vowel, and so of universal pronunciation, are only half as frequent. There are localities where the normal vibration of the tip of the tongue is replaced by one of the uvula, making a guttural trill, which is still more entitled to the name of "dog's letter" than is the ordinary r; such are considerable parts of France and Germany; the sound appears to occur only sporadically in English pronunciation. [Century Dictionary] 

Louise Pound ("The Humorous 'R'") notes that in British humorous writing, -ar- "popularly indicates the sound of the vowel in father" and formations like larf (for laugh) "are to be read with the broad vowel but no uttered r."

The moment we encounter the added r's of purp or dorg in our reading we know that we have to do with humor, and so with school-marm. The added consonants are supposed to be spoken, if the words are uttered, but, as a matter of fact, they are less often uttered than seen. The words are, indeed, largely visual forms; the humor is chiefly for the eye. [Louise Pound, "The Humorous 'R,'" American Mercury, October 1924]

H.A. Shands ("Some Peculiarities of Speech in Mississippi," 1893) notes uh as "The common negro form for the indefinite article a," and adds, "This is generally written er by dialect writers but no sound of r is ever apparent in the negro pronunciation." 

Louise Pound also quotes Henry James on the characteristic prominence of the medial -r- sound (which tends to be dropped in England and New England) in the speech of the U.S. Midwest, "under some strange impulse received toward consonantal recovery of balance, making it present even in words from which it is absent, bringing it in everywhere as with the small vulgar effect of a sort of morose grinding of the back teeth."

 In a circle, meaning "registered (trademark)," attested by 1925. R&R "rest and relaxation," is attested by 1953, American English; R&B "rhythm and blues" (type of popular music) is attested by 1949, American English. Form three Rs, see Three Rs.

"hawk-headed sovereign sun god of Egyptian mythology," from Egyptian R' "sun, day."

Ethiopian title of chief ministers, generals, governors, etc., from Amharic ras "chief, head," from Arabic ra's.

Moroccan capital, from Arabic ar-ribat, from ribat "fortified monastery."

"rectangular groove or channel cut out of the edge of a board or piece of stone so that it will join by overlapping with the next piece, similarly cut," late 14c., rabet, from Old French rabat "a recess in a wall, a lower section," literally "a beating down or back," a back-formation from rabattre "to beat down, beat back" (see rebate (v.); the noun is a doublet of this word).

The verb, meaning "to groove or fit (boards, etc.) by cutting rabbets" is attested from mid-15c. (implied in rabatted, rabetynge); Middle English also had rabet "joiner's plane, rabbet-plane" (mid-15c., from Old French rabot).

"Jewish doctor of religious law," early 14c. (in late Old English in biblical context only, as a form of address); in Middle English as a title prefixed to personal names, also "a spiritual master" generally; from Late Latin rabbi, from Greek rhabbi, from Mishnaic Hebrew rabbi "my master."

This is formed from -i, first person singular pronominal suffix, + rabh "master, great one," title of respect for Jewish doctors of law. This is from the Semitic root r-b-b "to be great or numerous" (compare robh "multitude;" Aramaic rabh "great; chief, master, teacher;" Arabic rabba "was great," rabb "master").

"pertaining to rabbis or their language, learning, or opinions," 1620s, earlier rabbinic (1610s); see rabbi + -ical. The -n- is perhaps via rabbin "rabbi" (1520s), an alternative form, from French rabbin or directly from Medieval Latin rabbinus (also source of Italian rabbino, Spanish and Portuguese rabino), perhaps from a presumed Semitic plural in -n, or from Aramaic rabban "our teacher," "distinguishing title given to patriarchs and the presidents of the Sanhedrin since the time of Gamaliel the Elder" [Klein], from Aramaic plural of noun use of rabh "great."

"dignity or office of a rabbi," 1702, from rabbin "rabbi" (see rabbinical) + -ate (1).

common burrowing mammal, identified as a rodent, noted for prolific breeding, late 14c., rabet, "young of the coney," suspected to be from Walloon robète or a similar northern French dialect word, a diminutive of Flemish or Middle Dutch robbe "rabbit," which are of unknown origin. "A Germanic noun with a French suffix" [Liberman]. The adult was a coney (q.v.) until 18c.

Zoologically speaking, there are no native rabbits in the United States; they are all hares. But the early colonists, for some unknown reason, dropped the word hare out of their vocabulary, and it is rarely heard in American speech to this day. When it appears it is almost always applied to the so-called Belgian hare, which, curiously enough, is not a hare at all, but a true rabbit. [Mencken, "The American Language"]

Rabbit punch "chop on the back of the neck" (1915) is so called from resemblance to a gamekeeper's method of dispatching an injured rabbit. Pulling rabbits from a hat as a conjurer's trick recorded by 1843. Rabbit's foot "good luck charm" is attested by 1879 in U.S. Southern black culture. Earlier references are to its use as a tool to apply cosmetic powders.

[N]ear one of them was the dressing-room of the principal danseuse of the establishment, who was at the time of the rising of the curtain consulting a mirror in regard to the effect produced by the application of a rouge-laden rabbit's foot to her cheeks, and whose toilet we must remark, passim, was not entirely completed. [New York Musical Review and Gazette, Nov. 29, 1856]

Rabbit-hole is by 1705. Rabbit ears "dipole television antenna" is from 1950. Grose's 1785 "Dictionary of the Vulgar Tongue" has "RABBIT CATCHER. A midwife."

c. 1300, "pack of animals" (a sense now obsolete), of uncertain origin, but possibly related to Middle English rablen "to gabble, speak in a rapid, confused manner" (mid-14c.), which is probably imitative of hurry, noise, and confusion (compare Middle Dutch rabbelen, Low German rabbeln "to chatter").

The meaning "tumultuous crowd of vulgar, noisy people" is from late 14c., probably a back-formation from the Middle English verb. It was applied contemptuously to the common or low part of any populace, regardless of tumult, by 1550s.