From ye olde OED:
[a. Pers. darvêsh, darvîsh poor, a religious mendicant, a friar, in Arab. darwêsh, darwîsh, Turkish dervîsh, the latter being the immediate source of the European forms: cf. It. dervis, F. dervis, derviche (in 1559 derviss), Sp. derviche, Ger. derwisch. Some of the variant spellings represent Arabic and Persian forms of the word. (The native Arabic equivalent is faqîr poor, fakir.)]
A Muslim friar, who has taken vows of poverty and austere life. Of these there are various orders, some of whom are known from their fantastic practices as dancing or whirling, and as howling dervishes.
Hence 'dervishhood, the estate or condition of a dervish. 'dervishism, the principles and practice of the dervishes; the dervish system. 'dervish-like a.