An Etymological Dictionary of the German Language/Annotated/Dom
Dom, masculine, ‘cathedral, dome, cupola,’ Modern High German only, borrowed from Latin domus (for domus dei; compare the Gothic word gudhûs, ‘the house of God, church’). An earlier loan-word is Old High German tuom (also dôm), Middle High German tuom, ‘a bishop's collegiate church, cathedral,’ which was naturalised in Germany about the 9th century; compare Old High German scuola from Latin scŏla, as if it were scôla; so tuom for tôm from dŏmus; see Schule. The form Tum, developed from Middle High German tuom, kept its ground till the beginning of the last century.