diaeresis
noun [ C ] mainly UK (US usually dieresis) uk/daɪˈer.ə.sɪs/ us/daɪˈer.ə.sɪs/ diaereses /daɪˈer.ə.siːz/ /daɪˈer.ə.siːz/
分音符，隔音符（指“¨”，表示两个元音须分别发音，如naïve）
a mark written over a vowel that shows it is pronounced separately from the vowel immediately before it, for example in the word naïve