isocline

/AY0 S AH0 K L AY0 N/
noun
  1. 1

    A tightly folded syncline or anticline in which the two sides are almost parallel

  2. 2

    Any of a series of lines having the same slope

  3. 3

    A line on a map linking places with the same magnetic dip

Source: https://en.wiktionary.org/wiki/isocline