before vowels mult-, word-forming element meaning "many, many times, much," from combining form of Latin multus "much, many," from PIE *ml-to-, from root *mel- (2) "strong, great, numerous." It was much-used in forming Latin compounds in classical times and after (such as multianimis "having much courage," multibibus "much-drinking," multicomus "having much hair," multiloquus "talkative"). Many English words that use it (multinational, etc.) are 20c. coinages.
1753, "consisting of or resembling cells," with reference to tissue, from Modern Latin cellularis "of little cells," from cellula "little cell," diminutive of cella "small room" (see cell). Of mobile phone systems (in which the area served is divided into "cells" of a few square miles served by transmitters), 1977. Related: Cellularity.
<a href="https://www.etymonline.com/word/multicellular">Etymology of multicellular by etymonline</a>
Harper, D. (n.d.). Etymology of multicellular. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/multicellular