Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
slack [slæk] adj (rope) прови́сший; (trousers) вися́щий; (discipline) сла́бый*слаб (security) плохо́й*плох (market) вя́лый; (demand) небольшо́й
n (in rope etc) слабина́
slacks
npl (trousers) сла́керсы pl
business is slack в дела́х засто́й
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.