31. Hiatus is the pronunciation of an initial vowel immediately after a final vowel. This was avoided, especially in poetry, by care in choosing and arranging words and by ν movable (§ 41), and was evaded or softened by elision and crasis.
Meagan Ayer, ed. Goodell’s School Grammar of Attic Greek. Carlisle, Pennsylvania: Dickinson College Commentaries, 2018. ISBN: 978-1-947822-10-8.https://dcc.dickinson.edu/grammar/goodell/hiatus