/kom"euh/, n.1. the sign (,), a mark of punctuation used for indicating a division in a sentence, as in setting off a word, phrase, or clause, esp. when such a division is accompanied by a slight pause or is to be noted in order to give order to the sequential elements of the sentence. It is also used to separate items in a list, to mark off thousands in numerals, to separate types or levels of information in bibliographic and other data, and, in Europe, as a decimal point.2. Class. Pros.a. a fragment or smaller section of a colon.b. the part of dactylic hexameter beginning or ending with the caesura.c. the caesura itself.3. Music. the minute, virtually unheard difference in pitch between two enharmonic tones, as G# and Ab.4. any of several nymphalid butterflies, as Polygonia comma, having a comma-shaped silver mark on the underside of each hind wing.[1520-30; < LL: mark of punctuation, L: division of a phrase < Gk kómma piece cut off (referring to the phrase so marked), equiv. to kop- (base of kóptein to strike, chop) + -ma n. suffix denoting result of action (with assimilation of p)]
* * *▪ musicin music, slight difference in frequency (and therefore pitch) occurring when a note of a scale, say E in the scale of C, is derived according to different systems of tuning (tuning and temperament). There are two commonly cited commas, the Pythagorean comma and the comma of Didymus, or syntonic comma.In Pythagorean tuning, the intervals of the scale are derived from natural fifths (the interval that occurs between the second and third tones of the harmonic series). When natural fifths are constructed in sequence, as from C to G to D. . . , a circle back to C (=B♯) occurs: . . . A♯, E♯, B♯. This B♯, however, instead of being exactly in tune with C, is slightly higher, by 0.24 of a semitone. This difference, which is audible, is the Pythagorean comma.Just intonation derives all intervals from natural fifths and natural thirds (the interval between the fourth and fifth tones of the harmonic series). A natural third is slightly lower than the third derived by Pythagorean tuning, which is disagreeable to Western ears. The difference is the comma of Didymus, or syntonic comma, and equals 0.22 of a semitone.
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