The Collaborative International Dictionary of English v.0.48:

Jan \Jan\ (j[a^]n), n. [Ar.] (Moham. Myth.)
   One of an intermediate order between angels and men.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Jan
    n 1: the first month of the year; begins 10 days after the
         winter solstice [syn: January, Jan]