antimeridian

[ an-tee-muh-rid-ee-uhn, an-tahy‐ ]

noun

1. the geographic meridian that lies 180° both east and west of the prime meridian, forming the great circle that divides the earth into the Eastern Hemisphere and the Western Hemisphere and serves as the meridian on which the International Date Line is based.

Word History and Origins

Origin of antimeridian¹

First recorded in 1810–15; anti- ( def ) + meridian ( def )