yogin (Sanskrit). A practitioner of yoga, a female practitioner being known as a yoginī. The term is commonly applied to practitioners of tantric Buddhism who engage in intensive meditational and ritual practice for long periods of time in caves or other isolated sites. The Six Yogas of Nāropa provide an example of these practices.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

Yogin (adj. -- n.) [fr. yoga, cp. Class. Sk. yogin] 1. ( -- ˚) applying oneself (to), working (by means of), using Vism 70 (hattha˚ & patta˚ using the hand or the bowl; but trsln p. 80: "hand -- ascetic" & "bowl -- ascetic"). <-> 2. one who devotes himself to spiritual things, an earnest student, one who shows effort (in contemplation), a philosopher, wise man. The word does not occur in the four Nikāyas. In the older verses it is nearly synonymous with muni. The oldest ref. is Th 1, 947 (pubbake yogī "Saints of other days" Mrs. Rh. D.). Freq. in Miln, e. g. pp. 2, 356 (yogi -- jana); at pp. 366, 393, 404, 417, 418 in old verses. Combd with yogâvacara Miln 366, 404. -- Further passages are Nett 3, 10, 61; Vism 2, 14, 66, 71 (in verse), 150, 320, 373, 509, 620, 651, 696; DhsA 195, 327.

Pali-English Dictionary, TW Rhys Davids, William Stede,