Definition of dieresis in US English:

dieresis

(also diaeresis)

noun

  • 1A mark (¨) placed over a vowel to indicate that it is sounded in a separate syllable, as in naïve, Brontë.

    • ‘No diacritic marks are normally used for native English words, unless the apostrophe and the diaeresis sign are counted as such.’
    • ‘This misspelling had been tackled earlier by Chast, who pointed out that Laennec, a native of Brittany, did not write his name with a diaeresis in his publications.’
    • ‘The New Yorker is probably the last popular magazine in the English-speaking world where the editors insist on the diaeresis (not umlaut) in ‘cöoperate’.’
    • ‘As several commenters have pointed out, both publications insist on using the diaeresis mark (as in naïve, for example) even though it hasn't been in common usage for several decades at least.’
    1. 1.1 The division of a sound into two syllables, especially by sounding a diphthong as two vowels.
  • 2Prosody
    A natural rhythmic break in a line of verse where the end of a metrical foot coincides with the end of a word.

Origin

Late 16th century (denoting the division of one syllable into two): via Latin from Greek diairesis ‘separation’, from diairein ‘take apart’, from dia ‘apart’ + hairein ‘take’.

Pronunciation

dieresis

/dīˈerəsəs//daɪˈɛrəsəs/