An end-of-meal sweet treat termed "dessert" (a) originated as a word from the notion of such following the main course plates being cleared away or "taken out of service."
Someone's getting "what is deserved" or "just deserts" (b) refers to that which is merited -- for better or worse -- from the quality of "service" provided to a superior or a benefactor.
Someone who "deserts" (c) or abandons obligations (as in military duties) is separating him/herself from the expected (suitable) procedures. This "desert" (d) also is basic to the designation of a barren, dry, and desolate area often of sandy terrain with sparse rainfall -- an uninviting place of abandonment -- "away from" the usual accessibility to water, food, and shelter.
The first two above-noted forms are related to "serve" and the latter two to "set apart" while also there are these various pronunciations: a. dee-ZURT b. dee-ZURTS c. dee-ZURTS d. DEH-zert. Confusion may result from the differences of concepts not fully corresponding to differences of forms.
However, someone traveling through a large arid area (on a camel, perhaps) could have food in prepared packets which could include dried meat and dried figs, the latter thus constituting a "dessert in the desert."
Many large arid areas have foreign-sounding names as most are found in regions far from North America -- with two exceptions as noted below.
The Mojave or Mohave (pronounced "moe-hah-vee") Desert is located southwest of Las Vegas, Nevada between there and Los Angeles, California and having a northern section comprising the infamous Death Valley of Old West folklore. The name is a Spanish version for a local native tribe meaning "Those Beyond the Water."
The Sonoran Desert is located in the coastal areas of U.S. and Mexico around the Gulf of California and extending northeast into Arizona ("Arid/Dry Zone"). The desert's name is likely a version of the Spanish term "Senora" as part of the 1533 designation for a local settlement by explorer Captain Diego de Guzman for the day of discovery being October 7 as then the Roman Catholic Feast Day of "Nuestra Senora del Rosario" (Our Lady of the Rosary).
Let's now consider names of other major deserts.
Sahara of North Africa -- the world's largest desert at 9,400,000 sq. km. from an Arabic source meaning "dry land."
Gobi of northern China and Mongolia -- from a Chinese term also meaning "dry land."
Kalahari of Botswana, Africa (actually a semi-desert) -- from the Tswana language meaning "Place of Great Thirst." "Botswana" means "Homeland of the Tswana."
Namib of Namibia along the Atlantic coast of Southern Africa -- from the Nama language meaning "Vast (Barren) Place."
Finally, adjacent deserts of an area north of Iran and Afghanistan: Karakum of central Turkmenistan -- from Turkic meaning "Black Sand Region" (from volcanic lava); and Kyzylkum of central Uzbekistan -- from Turkic meaning "Red Sand Region."