Does scansion ever require synizesis of two similar vowels?

Question

Does scansion ever require a synizesis like ŭŭ > ū or with u replaced by another vowel? I am not sure if this should be called synizesis when the two joined vowels have the same quality, but I hope my intention is clear enough. Here is an artificial example of a hexameter verse:

Est suus cuique viro canis et bene doctus amicus.
Every man has his dog and a well educated friend.

To be able to read this as hexameter, one is forced to make the synizesis ŭŭ > ū.

There was a question about confusion between ŭŭ and ū, but this one is about synizesis instead. An answer to the linked question mentions ĭĭt > īt. If someone can provide a line where īt is used and ĭĭt would invalidate the metric, that would make a nice answer, although I prefer spelling with two vowels if possible.

Answer 1

Here's an example from Lucan's Bellum civile (8.321) where īt is used and ĭĭt would break the meter:

nomen abit aut unde redi maiore triumpho? (8.321)

The form abiit would produce three short syllabus in a row.

Answer 2

The word "sŭŭs" is always counted as a sequence of two distinct vowels in latin hexameter, as you can see, for example, in Verg. georg. 4,190:

In noctem, fessosque sopōr sŭŭs ōccŭpăt artus

in Ov. ars 2,643:

Nēc sŭŭs Andromedae color est obiectus ab illo

and in Ov. met. 2,186, which has sŭūs just like your verse:

Frēnă sŭūs rector, quam dis uotisque reliquit

In your case, however, the sequence "ēst sŭūs cuique" (where -ūs is long as a closed syllable because of the following cuique) will result in a cretic (— ∪ —), a metrical sequence that is inadmissible inside the pattern of the hexameter.

You can make some searches using the database of http://www.mqdq.it, which is very useful in this sense.

Even more accurate is the search engine of http://www.pedecerto.eu/ricerca/forma, which shows the metrical patterns.

Answer 3

Synizesis of ee is supposed to occur in forms of the verb deesse. Presumably the result was [eː], with the same pronunciation as ē. This seems very similar to the contraction seen in words like dēbeo or dēmo.

Evidence from poetry indicates that those imperfective forms of deesse ‘be missing, absent’ where the stem begins with [e] are contracted even if the writing does not normally indicate it (i.e. deesse INF, deerat 3SINGPASTIMPF etc. are disyllabic, deest 3SINGPRESIMPF is monosyllabic).

(András Cser, "Aspects of the Phonology and Morphology of Classical Latin", 2016, p.147)

TKR left a comment mentioning an example of deerunt: "Martial (Epigrams, 8,56): Sint Maecenates, non deerunt, Flacce, Marones."

In a comment, blagae mentions that we also see synizesis of ee in the word deerraverat: "Verg. Buc. 7, 7: vir gregis ipse caper deerraverat; atque ego Daphnim"

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Note: there are apparently rare cases in Latin of the spelling ee being used to represent a long E sound even in words where it was not the result of synizesis of originally separate E's. There are examples in the following answers from Vladimir F and Alex B.