diaeresis

In linguistics, a diaeresis, also spelled dieresis (from Greek διαίρεσις, diairein, to divide; see also American and British spelling differences) is the pronunciation of two adjacent vowels in two separate syllables rather than as a diphthong. An example is the first two vowels in the word "coöperate". The opposite phenomenon is known as synaeresis.
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(n.)
Alt. of Dieresis
  

N F
distribution; G:breaking one syllable into two

Noun
1. a diacritical mark (two dots) placed over a vowel in German to indicate a change in sound
(synonym) umlaut, dieresis
(hypernym) diacritical mark, diacritic