([b.]) In many prepositional compounds when the members were still felt to be independent: as, praeesse (the contracted form praesse is found in inscriptions); dēerunt, they will be wanting, by the side of dērunt; coalēscō, grow together (the contracted form cōlēscō appears in Varro); cooptāre, coöpt, cooperiō, I cover up (by the side of rare cōptāre, cōperīre); coïtus, meeting, by the side of coetus ([120]).
([c.]) A comparatively large number of vowel combinations remain unchanged: as ea and eā in eam, her, and meā, by my (fem. sing.); ia and iā in māria, seas, viātōris, of the traveller; ua and uā in bēlua, monster, suā, through her (fem. sg.); iē in quiēs, quiet; uē in luēs, pestilence; eī in meī, of me; uī in tuī, of thee; eō in meō, by my (masc. sing.).
[117]. Synizesis. In these combinations the first vowel is sometimes made unsyllabic ([83]). This is called synizesis ([2499]) and is not rare in poets, being often the only means of adapting a word to the requirements of certain metres. Thus, fortuītus (- ⏑ - ⏓) must appear in a hexameter as fortvītus (fortṷītus). See [2499], [2503].
[118]. Contraction. ([1.]) Two like vowels may unite in one long vowel; rapidity of utterance was favourable to such fusion. In compounds, the desire to keep the members distinct often prevented it. So always nēmō, nobody, for *neemō from *ne-hemō, no man (for the loss of h, see [58], [150]; for e in *hemō, see [144]); and by the side of the open forms, nīl from nihil, nothing; vēmēns from vehemēns, rapid (connected with the verb vehō); rarely dērunt, they will be wanting, and dēsse, to be wanting, for dēerunt, dēesse; dēlēram, I had destroyed, from *dēlēeram for dēlēveram (for the loss of v, see [153]), see [890]; passūm, of paces, for passuum ([591]).
([2.]) A diphthong absorbs the following vowel: as, praetor, older praitor, praetor, from *prai-itor, who goes before; inscriptions show praerunt for praeerunt, they will be before; for praebēre, to furnish, the open form praehibēre occurs in Plautus ([1004]).
([3.]) If two unlike vowels are contracted at all, they usually unite in the long sound of the first vowel. Thus, o and a yield ō: as, cōgō, I force, from co-agō; cōgitō, I think, from co-agitō. Similarly Varro has cōlēscat, it may combine, for co-alēscat. o and e yield ō: as, prōmō, bring out, cōmō, put up, for pro-emō, co-emō ([953]). ē and a yield ē: as, dēgō, I pass away, from dē-agō ([937]). i and e in the termination of the vocative of -io- stems probably contracted to -ī; as fīlī from *fīlie, [459]. But in denominative ([365]) and other verbs of the first conjugation ā and ō contract into ō: as, amō, I love, from *amā-ō (cf. Greek τιμά·ω); and ā and ē into ē: as, amēs, thou mayest love, for *amā-ēs.
[119.] Elision. Only rarely the first of two successive vowels is dropped: as, nūllus, no, for *ne-ūllus; likewise the final vowel of the first member of nominal compounds: as, multangulus, with many corners, for *multi-angulus (cf. multi-cavus, with many holes); flexanimus, heart-rending, for *flexi-animus (cf. flexi-pēs, with bent feet).
[120.] Combination into diphthongs. The union of two successive vowels into a diphthong is equally rare: o and i are combined to oi, oe, in coetus, meeting, by the side of the open form coïtus ([116, b]); the perfect coepī ([812]), I began, owes its diphthong oe to forms in which the e was short and unaccented, such as the rare present forms coepiō for có-ĕpiō ([813]); for coḗpi ([813], [863]) would have remained unchanged ([116, a]). neuter, with the accent on the e, was pronounced as three syllables, later eu became diphthongal; neutiquam with synizesis ([117]) of e. e and ī̆ sometimes contract to e͡i in rēi ([601], [602]) and in de͡inde, dēin in the classic poets.
[121]. Compensative lengthening. When certain groups of consonants are simplified by the dropping of a consonant, its time is absorbed by a preceding short vowel, which thereby becomes long. This is called Compensation. In many cases compensative lengthening is due to the loss of a preliterary sonant s ([170, 2]): as,