Di·ær·e·sis, Di·er·e·sis  n.; pl. Diæreses or Diereses
  1. Gram. The separation or resolution of one syllable into two; -- the opposite of synæresis.
  2. A mark consisting of two dots [¨], placed over the second of two adjacent vowels, to denote that they are to be pronounced as distinct letters; as, coöperate, aërial.
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  dieresis
       n : a diacritical mark (two dots) placed over a vowel in German
           to indicate a change in sound [syn: umlaut, diaeresis]
       [also: diereses (pl)]