Familiarity, n.; pl. Familiarities.
Etymology: [OE. familarite, F. familiaritéfr. 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.
Shades of meaning
Fernald has no entry of its own for familiarity; he lists it under acquaintance, association.
Where he writes about it:
Acquaintance admits of many degrees, from a slight or passing to a familiar or intimate acquaintance; but acquaintance unmodified commonly signifies less than familiarity or intimacy. — from acquaintance
As regards persons, familiarity is becoming restricted to the undesirable sense, as in the proverb, "Familiarity breeds contempt;" hence, in personal relations, the word intimacy, which refers to mutual knowledge of thought and feeling, is now uniformly preferred. — from acquaintance
As regards studies, pursuits, etc., acquaintance is less than familiarity, which supposes minute knowledge of particulars, arising often from long experience or association. — from acquaintance