synaeresis

synaeresis [CL < συναίρεσις], joining or bringing together, union. b (prosod.) coalescing of two syllables into one, typically by the pronunciation of successive heterosyllabic vowels as a single diphthong. a junynge, compages, junctura, scinderesis [l. sineresis] CathA.  b dici per sineresim tibicen testatur, / metaplasmi species infra demoratur Qui majora cernitis 13; diptongus hujus diccionis Mnesteus faciat unam syllabam per suneresim Bacon Gram. Gk. 38; syncresis [l. syneresis] quando due syllabe coeunt in unam Ib. 65.

sўnærĕsis, is, f. (συναίρεσις), synérèse, contraction de deux voyelles en une diphtongue : Serv. B. 6, 78.