the mark ¨, in writing placed over the second of two adjacent vowels to indicate that it is to be pronounced separately rather than forming a diphthong with the first, as in some spellings of coöperate, naïve, etc
this mark used for any other purpose, such as to indicate that a special pronunciation is appropriate to a particular vowel Compare umlaut
a pause in a line of verse occurring when the end of a foot coincides with the end of a word
diaeretic, dieretic (ˌdaɪəˈrɛtɪk) adjective
C17: from Latin diarēsis, from Greek diairesis a division, from diairein, from dia- + hairein to take; compare heresy
also diaeresis, 1610s, "sign marking the division of a diphthong into two simple sounds," from Late Latin diaeresis, from Greek diairesis "division," noun of action from diairein "to divide, separate," from dia- "apart" (see dia-) + hairein "to take" (see heresy).