Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
knot [nɔt] n (also NAUT) у́зел#; (in wood) сучо́к#
vt завя́зывать (завяза́ть*perf) узло́м
to tie/untie a knot завя́зывать (завяза́ть*perf)/развя́зывать (развяза́ть# perf) у́зел
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.