Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
compulsory [kəmˈpʌlsərɪ] adj (attendance) обяза́тельный*обяза́телен (redundancy) принуди́тельный*принуди́телен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.