Origin and history of plio-

in geology, in reference to the most recent division of the Tertiary, 1833, from plio- "more" (Latinized form of pleio-) + -cene "recent." Execrated by classical purists (along with Miocene and Eocene); a proper form from Greek would be *Plionocene. Roughly 5.3 million to 2.6 million years ago, it is distinguished from the other two epochs by having more fossils of still-existing species. The Pliocene and the more recent Pleistocene, both comparatively brief, commonly now are combined as the Plio-Pleistocene. 

also pleo-, word-forming element meaning "more," from Greek pleiōn "larger, greater in quantity, the more part, very many" (comparative of polys "much"), from PIE *ple- (source also of Latin plere "to fill," plebes, "the populace, the common people;" Greek plēthein "be full," plērēs "full"), possibly a variant of root *pele- (1) "to fill."