An Etymological Dictionary of the German Language/Annotated/Küster
Küster, masculine, ‘sacristan,’ from the equivalent Middle High German and Old High German kustor, kuster, masculine. Adopted on the introduction of Christianity. While Kreuz, from Old High German chrûzi, is based upon the Latin stem cruci-, accusative singular crucem (and not the nominative crux), Küster, on the other hand, is not derived from Latin custodem (stem custodi-), or even from the non. singular custos, since in the Old High German period the change of s into r no longer occurs. We have rather to proceed from an actually recorded Middle Latin custor, custorem, a rare variant of the more prevalent form custod-, which appears also in French coutre, Old French costre, ‘sacristan.’ Middle Latin custos (scil. ecclesiae), ‘warden, guardian of the church jewels, holy vessels, &c., presbyter singular clericus cui ecclesiae et templi cura incumbit.’ With the same sense Middle Latin costurarius, whence Old Saxon costarâri, as well as Modern High German dialectic Gusterer.