also multi-national, by 1921, "comprising or pertaining to many nations," from multi- + national. Originally with reference to states; later (by 1960) to corporations and organizations. As a noun, short for multinational corporation (itself attested by 1956), one having branches, offices, etc. in many countries, it is attested by 1971.
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.