synizesis

noun

syn·​i·​ze·​sis ˌsi-nə-ˈzē-səs 

: contraction of two syllables into one by uniting in pronunciation two adjacent vowels

Word History

Etymology

Late Latin, from Greek synizēsis, from synizein to sit down together, collapse, blend, from syn- + hizein to sit down; akin to Latin sidere to sit down — more at subside

First Known Use

1846, in the meaning defined above