Where murid names a specific legal-devotional relationship, a disciple bound by pledge to one living teacher, dervish names a much broader figure: anyone visibly living the Sufi path, whether formally initiated into an order's chain of transmission or not. The word entered English and other European languages through Persian and Ottoman Turkish contact, and travelers' accounts from the medieval and early modern periods use it indiscriminately for any wandering Muslim ascetic they encountered, initiated or otherwise, which is part of why the term reads looser in English than the more precise Arabic vocabulary of murid, sheikh and khalifa that actually governs an order's internal structure.
That looseness reflects something real inside the tradition too. Alongside the settled lodges of major orders such as the Chishtiyya and the Naqshbandiyya, medieval and early modern Islam produced genuinely itinerant dervish groups, the Qalandariyya prominent among them, who deliberately rejected settled lodge life, standard dress and, in the more extreme cases, conventional social norms entirely, wandering and begging as a spiritual discipline in its own right. J. Spencer Trimingham's survey of the orders treats these wandering dervish groups as a real and recurring current within organized Sufism rather than a fringe exception, distinct from, though never entirely separate from, the settled khanqah and tekke life of the major tariqas.