V. S. Apte, The Practical Sanskrit–English Dictionary. Look up any word of the Gita in Devanagari, IAST or Harvard-Kyoto, or browse the headwords letter by letter.
Entry तैर्थिक
तैर्थिकtairthikaAn ascetic.
Derived forms and compounds
-कः
An ascetic.
One who propounds a new religious or philosophical doctrine.
-कम् Holy water (such as that brought from a sacred bathingplace).