Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
unceremonious [ʌnsɛrɪˈməunɪəs] adj (abrupt, rude) бесцеремо́нный*бесцеремо́нен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: