c. 1400, "to, of, or in the west (of the sky or the earth)," from Old French occidental (14c.) and directly from Latin occidentalis "western," from occidentem (see occident). Meaning "of, pertaining to, or characteristic of the western regions of the earth (especially Western Europe and its derivative civilizations in the western hemisphere" (opposed to oriental), 1550s. As a capitalized noun meaning "a Western person" (opposed to Oriental) it is attested from 1823. Related: Occidentalism; occidentalist.
Those who inhabit (to us) the western regions of the world, and to express whom the English language wants a word, the opposite of Orientals; though word-coining be much condemned, I will venture to employ Occidentalsas substantive and say, (etc.) ["The Bee," 1823]