noun, feminine/si.ni.ze.zis/
synizesis (the fusion of two syllables into one without the formation of a recognized diphthong, especially to fit a certain poetic meter); synizesis (a dense clumping of chromosomes on one side of the nucleus of a cell, sometimes occurring prior to cell division); synizesis (occlusion of the pupil of the eye, resulting in loss of vision)
From Ancient Greek συνίζησις (sunízēsis, “a sitting together”).