Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
thorough [ˈθʌrə] adj (search, wash) тща́тельный*тща́телен (knowledge, research) основа́тельный*основа́телен (person) скрупулёзный*скрупулёзен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.