What is "agonic line"

Agonic \A*gon"ic\, a. [Gr. ? without angles; 'a priv. + ? an angle.] Not forming an angle.

Agonic line (Physics), an imaginary line on the earth's surface passing through those places where the magnetic needle points to the true north; the line of no magnetic variation. There is one such line in the Western hemisphere, and another in the Eastern hemisphere.

n. (context cartography navigation English) A line on a chart or map joining points of zero magnetic declination.

n. an imaginary line connecting points on the Earth's surface where the magnetic declination is zero