The Collaborative International Dictionary of English v.0.48:

C \C\ (s[=e])
   1. C is the third letter of the English alphabet. It is from
      the Latin letter C, which in old Latin represented the
      sounds of k, and g (in go); its original value being the
      latter. In Anglo-Saxon words, or Old English before the
      Norman Conquest, it always has the sound of k. The Latin C
      was the same letter as the Greek [Gamma], [gamma], and
      came from the Greek alphabet. The Greeks got it from the
      Ph[oe]nicians. The English name of C is from the Latin
      name ce, and was derived, probably, through the French.
      Etymologically C is related to g, h, k, q, s (and other
      sibilant sounds). Examples of these relations are in L.
      acutus, E. acute, ague; E. acrid, eager, vinegar; L.
      cornu, E. horn; E. cat, kitten; E. coy, quiet; L. circare,
      OF. cerchier, E. search.
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   Note: See Guide to Pronunciation, [sect][sect] 221-228.
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   2. (Mus.)
      (a) The keynote of the normal or "natural" scale, which
          has neither flats nor sharps in its signature; also,
          the third note of the relative minor scale of the
          same.
      (b) C after the clef is the mark of common time, in which
          each measure is a semibreve (four fourths or
          crotchets); for alla breve time it is written ?.
      (c) The "C clef," a modification of the letter C, placed
          on any line of the staff, shows that line to be middle
          C.
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   3. As a numeral, C stands for Latin centum or 100, CC for
      200, etc.
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   C spring, a spring in the form of the letter C.
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