The Collaborative International Dictionary
Isogonic lines
Isogonic \I`so*gon"ic\, a. [Iso- + Gr. gwni`a angle.] Pertaining to, or noting, equal angles.
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.