Diaeresis or dieresis (both pronounced /daɪˈɛrɪsɪs/ or /daɪˈɪərɪsɪs/) may refer to:
- Diaeresis (prosody), pronunciation of vowels in a diphthong separately, or the division made in a line of poetry when the end of a foot coincides with the end of a word
- Diaeresis (linguistics) or Hiatus, two adjacent vowels, in adjacent syllables, not separated by a consonant or pause and not merged into a diphthong
- Diaeresis (diacritic), a diacritic consisting of two dots that marks a hiatus
- Diaeresis (philosophy), a term in Platonic and Stoic philosophy