climate (n.) Look up climate at Dictionary.com
late 14c., "horizontal zone of the earth," Scottish, from Old French climat "region, part of the earth," from Latin clima (genitive climatis) "region; slope of the Earth," from Greek klima "region, zone," literally "an inclination, slope," thus "slope of the Earth from equator to pole," from root of klinein "to slope, to lean" (see lean (v.)).

The angle of sun on the slope of the Earth's surface defined the zones assigned by early geographers. Early references in English, however, are in astrology works, as each of the seven (then) climates was held to be under the influence of one of the planets. Shift from "region" to "weather associated with a region" perhaps began in Middle English, certainly by c.1600.