R.

2 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  R \R\ ([aum]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, [sect][sect] 178, 179, and
     250-254. "R is the dog's letter and hurreth in the sound."
     --B. Jonson.


     [1913 Webster]
  
     Note: 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 Ph[oe]nician, 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]

From WordNet (r) 2.0 [wn]:

  R
       n 1: a unit of radiation exposure; the dose of ionizing radiation
            that will produce 1 electrostatic unit of electricity in
            1 cc of dry air [syn: {roentgen}]
       2: (physics) the universal constant in the gas equation:
          pressure times volume = R times temperature; equal to
          8.3143 joules per kelvin per mole [syn: {gas constant}, {universal
          gas constant}]
       3: the 18th letter of the Roman alphabet
       4: the length of a line segment between the center and
          circumference of a circle or sphere [syn: {radius}]