"wasteland," early 13c., from Old French desert (12c.) "desert, wilderness, wasteland; destruction, ruin," from Late Latin desertum (source of Italian diserto , Old Provençal dezert , Spanish desierto ), literally "thing abandoned" (used in Vulgate to translate "wilderness"), noun use of neuter past participle of Latin deserere "forsake" (see desert (v.)).
Sense of "waterless, treeless region" was in Middle English and gradually became the main meaning. Commonly spelled desart in 18c., which is not etymological but at least avoids confusion with the other two senses of the word. Classical Latin indicated this idea with deserta , plural of desertus .