Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
dull [dʌl] adj (light, colour) ту́склый*тускл (weather, day) се́рый*сер (sound) глухо́й*глух (pain, wit) тупо́й*туп (event) ску́чный*ску́чен
vt притупля́ть (притупи́ть*perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.