What is "agonic"

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.

a. 1 (label en geometry) Lacking an angle. 2 (label en cartography navigation) Having a magnetic deviation of zero.