Definition of diaeresis in English:
noun (plural diaereses /-siːz/)
1A mark (¨) placed over a vowel to indicate that it is sounded separately, as in naïve, Brontë.
- 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.
- 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’.
- No diacritic marks are normally used for native English words, unless the apostrophe and the diaeresis sign are counted as such.
Definition of diaeresis in:
- US English dictionary