Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
incoherent [ɪnkəuˈhɪərənt] adj (argument) непосле́довательный*непосле́дователен (speech) несвя́зный*несвя́зен (person) косноязы́чный*косноязы́чен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: