Correption

In Latin and Greek poetry, correption (Latin: correptiō [kɔrˈrɛpt̪ioː], "a shortening") is the shortening of a long vowel at the end of one word before a vowel at the beginning of the next. Vowels next to each other in neighboring words are in hiatus.

Homer uses correption in dactylic hexameter:

• Ἄνδρα μοι ἔννεπε, Μοῦσα, πολύτροπον, ὃς μάλα πολλὰ
  πλάγχθη, ἐπεὶ Τροίης ἱερὸν πτολίεθρον ἔπερσε·
  — Odyssey 1.1-2
• Tell me, O Muse, of the man of many devices, who wandered full
  many ways after he had sacked the sacred citadel of Troy.
  — translation by A.T. Murray

Here the sequence η ε in bold must be pronounced as ε ε to preserve the long—short—short syllable weight sequence of a dactyl. Thus, the scansion of the second line is thus:

πλαγχ θε, ε | πει Τροι | η ςι ε | ρον πτο λι | εθ ρο νε | περ σε