Synonyms for Familiarity (same or very similar meaning)
WordNet sense 1 (personal knowledge or information about someone or something):
acquaintance, conversance, conversancyWordNet sense 2 (a casual manner):
casualnessWordNet sense 3 (close or warm friendship):
closeness, intimacyWordNet sense 4 (an act of undue intimacy):
impropriety, liberty, indecorumFrom the ODE community, based on WordNetadd/edit