Triliteral root D-R-B. Noun, Darb is not a word of Arabic origin. The Arab word for the ancient Derbe, near the Caspian Gates, which were the chief mountain pass from the direction of the countries occupied by the Arabs into the territory of the Greek Empire [of Rum]. Hence, Any place of entrance. Darboob, A she-camel that will follow a person if he takes hold of her lip or eyelash. Mudarrab, A camel well trained or accustomed to be ridden through narrow mountain passes.
-Lane’s Lexicon
…Daraw, a village on the Nile’s east bank, where if you are lucky you will see camels kicking up the dust…the end of the Darb al-Arba’een, the Forty Days Road.
-Insight Guides: The Nile
It is not strange to me that the Forty Days Road from Kordofan to Cairo that I followed twice was not the true Darb al-Arba’in, which more properly bypassed the Nile altogether following a string of oases until it reached Assiut, but rather that the Arabic word Darb comes from Persian [a shortening of the compound noun Darband, from Dar for Gate and Band for Bar, making Barred Gate, as in Derbent, the Caspian port city at the eastern edge of the Caucasus Mountains]. I would have thought that a quintessential Arab desert route would claim a quintessential Arabic language etymology.
But leave it to the medieval Arab grammarians, who never saw a useful foreign loan word they could not fit into their own Semitic language’s triliteral root system, to generate such rarefied camel-related cognates as Darboob and Mudarrab. I never heard those two words spoken on the darb, although we never saw the need to grab a she-camel by the eyelash while passing between two mountains.