A muni is a saint, sage, ascetic, or hermit. This is a traditional term found in the epics and the Puranas, superseding the earlier VEDIC term RISHI. It is still used in modern Hinduism, although somewhat less than the terms sadhu and swami. The Jain tradition (see JAINISM) uses the term muni for a respected monk.
Further reading: Patrick Olivelle, trans., Sannyasa Upa-nishads: Hindu Scriptures on Asceticism and Renunciation (New York: Oxford University Press, 1992).
Encyclopedia of Hinduism. A. Jones and James D. Ryan. 2007.