n. [ Iso- + Gr. gh^ the earth + qe`rmh heat. ] (Phys. Geog.) A line or curved surface passing beneath the earth's surface through points having the same mean temperature.

{ } a. Pertaining to, having the nature of, or marking, isogeotherms; as, an isogeothermal line or surface; as isogeothermal chart. -- n. An isogeotherm. [ 1913 Webster ]