diaeresis

treema, diereesi puhekieltä A diacritic ( ¨ ) placed over a vowel letter (especially the second of two consecutive ones) indicating that it is sounded separately, usually forming a distinct syllable, as in the English words (m), (m) and (m), the French (m) and the Dutch (m).
puhekieltä The separation of a vowel, often a diphthong, into two distinct syllables.
puhekieltä A natural break in rhythm when a word ends at the end of a metrical foot, in a line of verse.
puhekieltä (l) (gloss)
AD 98–138, (w) (aut.), w:Heinrich Keil|T.H.G. Keil (ed.), Liber de orthographia in Grammatici Latini VII (1880), p. https://archive.org/stream/grammaticilatini07keilpage/57/mode/1up 57, ll. 21–28:

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