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.
late 14c., "resembling a line," from Old French lineal "pertaining to a line" (14c.), from Late Latin linealis "pertaining to a line," from linea "a string, line, thread" (see line (n.)). Compare linear. Related: Lineally.
<a href="https://www.etymonline.com/word/multilineal">Etymology of multilineal by etymonline</a>
Harper, D. (n.d.). Etymology of multilineal. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/multilineal