Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ōmĭnōsus, a, um, adj. [omen], full of foreboding, portentous, ominous (post-Aug.): mons avibus obscenis ominosus, Messala ap. Gell. 13, 14, 6: res, Plin. Ep. 3, 14, 11.
Adv.: ōmĭnōsē, ominously: ominose retentus, Ps.-Quint. Decl. 6, 5.