dieresis

from WordNet (r) 3.0 (2006)

dieresis
    n 1: a diacritical mark (two dots) placed over a vowel in German
         to indicate a change in sound [syn: {umlaut}, {dieresis},
         {diaeresis}]

from The Collaborative International Dictionary of English v.0.48

Dieresis \Di*er"e*sis\, n. [NL.]
   Same as {Di[ae]resis}.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Diaeresis \Di*[ae]r"e*sis\, Dieresis \Di*er"e*sis\ (?; 277), n.;
   pl. {Di[ae]reses} or {Diereses}. [L. diaeresis, Gr. ?, fr. ?
   to divide; dia` through, asunder + ? to take. See {Heresy}.]
   1. (Gram.) The separation or resolution of one syllable into
      two; -- the opposite of syn[ae]resis.
      [1913 Webster]

   2. A mark consisting of two dots [[umlaut]], placed over the
      second of two adjacent vowels, to denote that they are to
      be pronounced as distinct letters; as, co["o]perate,
      a["e]rial.
      [1913 Webster]