plethora

Borrowed from Late Latin plēthōra, itself from Ancient Greek πληθώρα (plēthṓra), meaning "fullness, satiety." That Greek noun comes from the verb πλήθω (plḗthō), "to be full," plus the nominal suffix -η.

The facts don't trace a documented shift in meaning beyond its root sense of fullness or satiety, so it's honest to say the word has carried that core idea of "too much" from its Greek origin forward.

The facts given don't identify any specific English cognate, so none can be claimed here.