early 15c., "fullness, completeness, perfection," from Old French plenitude and directly from Latin plenitudinem (nominative plenitudo) "abundance, completeness, fullness," from plenus "full, filled, greatly crowded; stout, pregnant; abundant, abounding; complete," from PIE root *pele- (1) "to fill." Related: Plenitudinary.
<a href="https://www.etymonline.com/word/plentitude">Etymology of plentitude by etymonline</a>
Harper, D. (n.d.). Etymology of plentitude. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/plentitude