The Collaborative International Dictionary of English v.0.48:

Isogonic \I`so*gon"ic\, a. [Iso- + Gr. gwni`a angle.]
   Pertaining to, or noting, equal angles.
   [1913 Webster]

   Isogonic lines (Magnetism), lines traced on the surface of
      the globe, or upon a chart, connecting places at which the
      deviation of the magnetic needle from the meridian or true
      north is the same.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Isogonic \I`so*gon"ic\, a. (Zool.)
   Characterized by isogonism.
   [1913 Webster]

WordNet (r) 3.0 (2006):

isogonic
    adj 1: having or making equal angles