The Collaborative International Dictionary of English v.0.48:

Familiar \Fa*mil`iar\, a. [OE. familer, familier, F. familier,
   fr. L. familiaris, fr. familia family. See Family.]
   1. Of or pertaining to a family; domestic. "Familiar feuds."
      --Byron.

   Syn: familial.
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   2. Closely acquainted or intimate, as a friend or companion;
      well versed in, as any subject of study; as, familiar with
      the Scriptures.
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   3. Characterized by, or exhibiting, the manner of an intimate
      friend; not formal; unconstrained; easy; accessible. "In
      loose, familiar strains." --Addison.
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            Be thou familiar, but by no means vulgar. --Shak.
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   4. Well known; well understood; common; frequent; as, a
      familiar illustration.
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            That war, or peace, or both at once, may be
            As things acquainted and familiar to us. --Shak.
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            There is nothing more familiar than this. --Locke.
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   5. Improperly acquainted; wrongly intimate. --Camden.
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   Familiar spirit, a demon or evil spirit supposed to attend
      at call. --1 Sam. xxviii. 3, 7-9.
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WordNet (r) 3.0 (2006):

familiar spirit
    n 1: a spirit (usually in animal form) that acts as an assistant
         to a witch or wizard [syn: familiar, familiar spirit]