An Etymological Dictionary of the German Language/Annotated/-tum
-tum, suffix, from Middle High German and Old High German -tuom; an abstract suffix, which has been formed in compounds from an independent word tuom, masculine and neuter, ‘relation, rank, dignity, condition.’ This is an abstract form of Modern High German thun. Compare the corresponding English suffix -dom in kingdom. English has preserved the independent word doom (Anglo-Saxon dôm), to which to deem (Anglo-Saxon dêman) is allied; compare Sanscrit dhâman, ‘institution, sacred custom.’