-ˌthərm noun
( -s )
Etymology: French isotherme, adjective, isothermal, from is- + -therme (from Greek thermē heat, from thermos hot) — more at warm
1. : a line on a map or chart of the earth's surface connecting points having the same temperature at a given time or the same mean temperature for a given period
2. : a line on a chart representing changes of volume or pressure under conditions of constant temperature