Hello Jeff (and everyone else),
One of the great things about the internet is that it obviates ever having to look things up in a concrete dictionary. Since you're asking for characters, I presume you can read modern vernacular (putonghua) or classical (wenyan; "kanbun" in Japanese.) Literally "teacher of the Law," see:
http://baike.baidu.com/view/38907.htm Note the differences among "fashi" in Buddhism, Daoism, and then finally, as translated from the West. For specifically the Daoist version, see:
http://zh.wikipedia.org/wiki/%E9%81%93%E5%A3%AB I think one of my great aunts in Malaysia is fat-si. The religious situation in the family is quite complicated--my immediate family is Protestant--with Christianity, Islam, Buddhism, and Daoism/shamanistic beliefs all represented among relations. That noted, I'm not a believer and so I approach all of this as an outsider.
If you have some spare time, there's an interesting historical novel that provides lots of informative cultural background:
Eva Wong (trans.), _Seven Taoist Masters: a Folk Novel of China_ (Boston: Shambala Publications, 1990.)
http://www.amazon.com/Seven-Taoist-Masters...03128121&sr=8-1