kibbutz vs terramare

kibbutz

noun
  • A community, usually an agricultural one in Israel, based on a high level of social and economical sharing, equality, direct democracy and tight social relations. 

terramare

noun
  • Bronze Age lake dwellings and settlements of the Po valley in northern Italy, characterized by the presence of ammoniacal earthy deposit (black marl) in mounds. 

How often have the words kibbutz and terramare occurred in a corpus of books? (source: Google Ngram Viewer )