Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
attenuate [əˈtɛnjueɪt] vt ослабля́ть (осла́бить*perf)
vi ослабля́ться (осла́биться*perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.