hendecad
/ˌhɛnˈdɛkad/(also endecad, hendecade, endekad)
noun
A group, set, or series of eleven things; specifically (especially in Old English) a period of eleven years. Formerly also occasionally: †the number eleven (obsolete ).
Origin
Old English; earliest use found in Byrhtferð of Ramsey (fl. c986–c1016), Benedictine monk and scholar. From post-classical Latin hendecad-, hendecas and its etymon ancient Greek ἑνδεκάδ-, ἑνδεκάς the number eleven from ἕνδεκα eleven + -άς.