from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A line on a map connecting points of equal magnetic declination.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A line on a chart or map showing points of constant magnetic declination.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. an imaginary line connecting points on the Earth's surface where the magnetic declination is the same
isogonic + line (Wiktionary)