the tenure by which lands were held by a thane.
the land so held.
the office, rank, or jurisdiction of a thane.

Origin of thanage

First recorded in 1350–1400; Middle English word from Anglo-Latin word thanāgium. See thane, -age Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for thanage

c.1400, from Anglo-French thaynage (c.1300), from English thane + Old French suffix -age (see -age).

Online Etymology Dictionary, © 2010 Douglas Harper