The two dots above a continental ï (as, for example, in “naïf”), are called a diaeresis. When two or more are gathered together, they become diareses.

If you like this, you’ll love our resources about Greeks. Plain English Anatomy™ Noun | Verb | Adjective | Adverb | Preposition | Conjunction | Latin | Germany | Flannel | Legal triplicate | Nominalisation | Murder your darlings