Isotherm /(?)/

I·so·therm

Isotherm

n.
  1. A line connecting or marking points on the earth's surface having the same temperature. This may be the temperature for a given time of observation, or the mean temperature for a year or other period. Also, a similar line based on the distribution of temperature in the ocean. (Phys. Geog.)
  2. A line on a graph connecting points representing states having the same temperature; an isothermal line. (Physics)