The Collaborative International Dictionary of English v.0.48:

Pentangle \Pen"tan`gle\, n. [Penta- + angle.]
   A pentagon. [R.] --Sir T. Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pentangle
    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]