-r-

R, the eighteenth letter of the English alphabet, is a vocal consonant. It is sometimes called a semivowel, and a liquid. See Guide to Pronunciation, §§ 178, 179, and 250-254. “R is the dog's letter and hurreth in the sound.” B. Jonson. [ 1913 Webster ]

In words derived from the Greek language the letter h is generally written after r to represent the aspirated sound of the Greek "r, but does not affect the pronunciation of the English word, as rhapsody, rhetoric. [1913 Webster] The English letter derives its form from the Greek through the Latin, the Greek letter being derived from the Phœnician, which, it is believed, is ultimately of Egyptian origin. Etymologically, R is most closely related to l, s, and n; as in bandore, mandole; purple, L. purpura; E. chapter, F. chapitre, L. capitulum; E. was, were; hare, G. hase; E. order, F. ordre, L. ordo, ordinis; E. coffer, coffin. [1913 Webster]

The three Rs, a jocose expression for reading, (w)riting, and (a)rithmetic, -- the fundamentals of an education. [1913 Webster]