An Etymological Dictionary of the German Language/Annotated/Base

by Friedrich Kluge

Base, feminine (dialect. designating any of the remoter degrees of relation on the female side, e.g., in the Basle dialectic ‘aunt, niece, cousin’), ‘cousin, aunt,’ from Middle High German base, Old High German basa, ‘father's sister’; the Anglo-Saxon and Frisian dialects have a word allied to Vater; Anglo-Saxon faþu, Old Frisian fethe. The Teutonic type faþôn is certainly only a term of endearment for faþar-, fadar-suëstar, ‘father’s sister.’ Probably Old High German basa is also a pet or childish name for the proper badar-, fadar-swësô. The same might be said of the variant Middle German and Low German Wase, and with the necessary qualifications of the masculine Baas.