noun
magnetic meridian
Technical term in geomagnetism and navigation; the line on the Earth's surface connecting the magnetic poles along which a compass needle aligns.
磁気子午線は真の子午線とは少しずれている。
The magnetic meridian deviates slightly from the true meridian.
Compound of 磁気 (magnetism) + 子午線 (meridian). The exact historical derivation is uncertain; the term is a modern technical coinage.