*dem- Look up *dem- at Dictionary.com
Proto-Indo-European root meaning "house, household." It represents the usual Indo-European word for "house" (Italian, Spanish casa are from Latin casa "cottage, hut;" Germanic *hus is of obscure origin).

It forms all or part of: Anno Domini; belladonna; condominium; dame; damsel; dan "title of address to members of religious orders;" danger; dangerous; demesne; despot; Dom Perignon; domain; dome; domestic; domesticate; domicile; dominate; domination; dominion; domino; don (n.) "Spanish, Italian, and Portuguese title of respect;" Donna; dungeon; ma'am; madam; madame; mademoiselle; madonna; major-domo; predominant; predominate; timber; toft.

It is the hypothetical source of Sanskrit damah "house;" Avestan demana- "house;" Greek domos "house," despotes "master, lord;" Latin domus "house," dominus "master of a household;" Armenian tanu-ter "house-lord;" Old Church Slavonic domu, Russian dom "house;" Lithuanian dimstis "enclosed court, property;" Old Norse topt "homestead."