Source : Webster's Revised Unabridged Dictionary (1913)

Familiarity \Fa*mil`iar"i*ty\, n.; pl. {Familiarities}. [OE.
   familarite, F. familiarit['e]fr. L. faniliaritas. See
   {Familiar}.]
   1. The state of being familiar; intimate and frequent
      converse, or association; unconstrained intercourse;
      freedom from ceremony and constraint; intimacy; as, to
      live in remarkable familiarity.

   2. Anything said or done by one person to another
      unceremoniously and without constraint; esp., in the pl.,
      such actions and words as propriety and courtesy do not
      warrant; liberties.

   Syn: Acquaintance; fellowship; affability; intimacy. See
        {Acquaintance}.

Source : WordNet®

familiarity
     n 1: personal knowledge or information about someone or something
          [syn: {acquaintance}, {conversance}, {conversancy}]
     2: usualness by virtue of being familiar or well known [ant: {unfamiliarity}]
     3: close or warm friendship; "the absence of fences created a
        mysterious intimacy in which no one knew privacy" [syn: {intimacy},
         {closeness}]
     4: a casual manner [syn: {casualness}]
     5: an act of undue intimacy [syn: {impropriety}, {indecorum}, {liberty}]