"wasteland, wilderness, barren area," wooded or not, c. 1200, from Old French desert (12c.) "desert, wilderness, wasteland; destruction, ruin" and directly 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 of considerable extent" was in Middle English and gradually became the main meaning. Classical Latin indicated this idea with deserta, plural of desertus. Commonly spelled desart in 18c., which is unetymological, but it avoids confusion with the two other senses of the word.
Every important worker will report what life there is in him. It makes no odds into what seeming deserts the poet is born. Though all his neighbors pronounce it a Sahara, it will be a paradise to him; for the desert which we see is the result of the barrenness of our experience. [Thoreau, Journal, May 6, 1854]