adjective Mathematics Now Rare.
Examples from the Web for agonic
Agonic line, line along which the needle points due north and south.The Nuttall Encyclopaedia|Edited by Rev. James Wood
At present the motion of the agonic line seems to be towards the west, but it is very slow.
To the east of the agonic line the declination is westerly, and to the west it is easterly.
The line passing through points where the needle points north, without declination, is the agonic line.Physics|Willis Eugene Tower