desertyoudaoicibaDictYouDict[desert 词源字典]
desert: English has three distinct words desert, which come from two separate sources. Desert ‘what one deserves’ [13] (now usually used in the plural) is related, as its meaning suggests, to the verb deserve. It comes from Old French desert or deserte, which were formed from the past participle of deservir ‘deserve’. (Dessert ‘sweet course’ [17] is its first cousin, coming from French desservir ‘clear the table’ – literally ‘unserve’ – a compound verb formed, like deserve, from the verb serve but with the prefix dis- rather than de-.) The noun desert ‘barren region’ [13] and the verb desert ‘abandon’ [15] both come ultimately from dēsertus, the past participle of Latin dēserere ‘abandon’.

This was a compound verb formed from the prefix dē- denoting reversal and serere ‘join’ (a derivative of which gave English ‘serried ranks’).
=> serve; serried[desert etymology, desert origin, 英语词源]
desert (v.)youdaoicibaDictYouDict
"to leave one's duty," late 14c., from Old French deserter (12c.) "leave," literally "undo or sever connection," from Late Latin desertare, frequentative of Latin deserere "to abandon, to leave, forsake, give up, leave in the lurch," from de- "undo" (see de-) + serere "join together, put in a row" (see series). Military sense is first recorded 1640s. Related: Deserted; deserting.
desert (n.1)youdaoicibaDictYouDict
"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.
desert (n.2)youdaoicibaDictYouDict
"suitable reward or punishment" (now usually plural and with just), c. 1300, from Old French deserte, noun use of past participle of deservir "be worthy to have," ultimately from Latin deservire "serve well" (see deserve).