dieresis: Meaning and Definition of

di•er•e•sis

1. the separation of two adjacent vowels, dividing one syllable into two.
2. a sign (¨) placed over the second of two adjacent vowels to indicate separate pronunciation, as in one spelling of the older forms naïve and coöperate: no longer widely used in English.
3. the division made in a line or verse by coincidence of the end of a foot and the end of a word.