Fa·mil·iar a.
 1. Of or pertaining to a family; domestic. “Familiar feuds.”
 Syn: -- familial.
 2. Closely acquainted or intimate, as a friend or companion; well versed in, as any subject of study; as, familiar with the Scriptures.
 3. Characterized by, or exhibiting, the manner of an intimate friend; not formal; unconstrained; easy; accessible. “In loose, familiar strains.”
    Be thou familiar, but by no means vulgar.   --Shak.
 4. Well known; well understood; common; frequent; as, a familiar illustration.
 That war, or peace, or both at once, may be
 As things acquainted and familiar to us.   --Shak.
    There is nothing more familiar than this.   --Locke.
 5. Improperly acquainted; wrongly intimate.
 Familiar spirit, a demon or evil spirit supposed to attend at call.
 familiar spirit
      n : a spirit (usually in animal form) that acts as an assistant
          to a witch or wizard [syn: familiar]
 Familiar spirit
    Sorcerers or necormancers, who professed to call up the dead to
    answer questions, were said to have a "familiar spirit" (Deut.
    18:11; 2 Kings 21:6; 2 Chr. 33:6; Lev. 19:31; 20:6; Isa. 8:19;
    29:4). Such a person was called by the Hebrews an _'ob_, which
    properly means a leathern bottle; for sorcerers were regarded as
    vessels containing the inspiring demon. This Hebrew word was
    equivalent to the pytho of the Greeks, and was used to denote
    both the person and the spirit which possessed him (Lev. 20:27;
    1 Sam. 28:8; comp. Acts 16:16). The word "familiar" is from the
    Latin familiaris, meaning a "household servant," and was
    intended to express the idea that sorcerers had spirits as their
    servants ready to obey their commands.