isocline

Etymology
From.

Noun

 * 1)  A tightly folded syncline or anticline in which the two sides are almost parallel.
 * 2)  A line, curve or function on a graph or map linking points with the same slope or gradient.
 * 3)  A line on a map linking places with the same magnetic dip; an isoclinic line.

Translations

 * Icelandic: jafnhallaferill
 * Russian: