Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
dormant [ˈdɔːmənt] adj (plant) поко́ящийся; (volcano) спя́щий; (idea, report etc)
to lie dormant безде́йствовать (impf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.