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Related to agonic line: aclinic line, Isogonic lines
a·gon·ic line(ā-gŏn′ĭk, ə-)
An imaginary line on the earth's surface connecting points where the magnetic declination is zero.
[Greek agōnos, having no angle (a-, without; see a-1 + gōniā, angle; see diagonal) + -ic.]
(General Physics) an imaginary line on the surface of the earth connecting points of zero magnetic declination
A line drawn on a map or chart joining points of zero magnetic declination for a specified year date. See also magnetic declination.