Webster’s Revised Unabridged Dictionary · 1913
Isogonic
I′so·gon′ic (·gŏn′ĭk), a. [Iso- + Gr. γωνία 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.
I′so·gon′ic, a. (Zoöl.) Characterized by isogonism.