I'so-thēre, n.
n. [Gr. ἴσος, equal, and θέρος, summer.] (Phys. Geog.) An imaginary line over the earth's surface, passing through points having the same mean summer temperature. Nichol.
n. [Gr. ἴσος, equal, and θέρος, summer.] (Phys. Geog.) An imaginary line over the earth's surface, passing through points having the same mean summer temperature. Nichol.