In the 14th century, the monk Robert of Brunne described a situation in which all the knights of King Arthur's Round Table were present at court by writing, "When Arthures court was plener, and alle were comen, fer and ner.…" For many years, plener (also spelled plenar) served English well for both senses that we reserve for plenary today. But we'd borrowed plener from Anglo-French, and, although the French had relied on Latin plenus ("full") for their word, the revival of interest in the Classics during the English Renaissance led scholars to prefer purer Latin origins. In the 15th century, English speakers turned to Late Latin plenarius and came up with plenary. (Plenarius also comes from plenus, which is the source of our plenty and replenish as well.)