\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.