The Collaborative International Dictionary of English v.0.48:

Pentagram \Pen"ta*gram\, n. [Gr. ?, neut. of ? having five
   lines. See Penta-, and -gram.]
   A pentacle or a pentalpha. "Like a wizard pentagram."
   --Tennyson.
   [1913 Webster] Pentagraphic

WordNet (r) 3.0 (2006):

pentagram
    n 1: a star with 5 points; formed by 5 straight lines between
         the vertices of a pentagon and enclosing another pentagon
         [syn: pentacle, pentagram, pentangle]