Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
adequate [ˈædɪkwɪt] adj (sufficient) доста́точный/доста́точен (satisfactory) удовлетвори́тельный*удовлетвори́телен , адеква́тный*адеква́тен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.