dieresis (): a diacritic mark written above a vowel, commonly used by linguists in the Americas to create new vowel symbols. The vowel with dieresis is identical to the vowel without dieresis, except that the tongue position changes from back to front or vice versa. For example, when a dieresis is added to the vowel o, which is back, mid [1], and round, the result (ö) is front, mid and round. When a dieresis is added to the vowel i, which is front, high, and unrounded, the result (ï) is back, high [1], and unrounded. (See the diagram of phonetic symbols for vowels.) [Spanish: diéresis]