1610s, erroneous form of plenitude, probably by influence of plenty, etc.
Entries linking to plentitude
plenitude n.
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.