Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

pernĭcĭōsus, a, um, adj. [pernicies], destructive, ruinous, baleful, pernicious (syn.: exitialis, capitalis): perniciosae leges, Caes. B. C. 1, 7: scripta auctori perniciosa suo, Ov. Tr. 5, 1, 68.
Comp.: morbi animi perniciosiores sunt, quam corporis, Cic. Tusc. 3, 3, 5; Sall. J. 46, 8.
Sup.: perniciosissimum fore, Nep. Ages. 6, 2; Inscr. Grut. 113, 2.
As subst.: pernĭcĭōsa, ōrum, n., baneful things: petuntur, Juv. 10, 54; cf.: inter perniciosissima numerare, Vell. 2, 7, 5.
Hence, adv.: pernĭcĭōsē, destructively, ruinously, perniciously: multa perniciose, multa pestifere sciscuntur in populis, Cic. Leg. 2, 5, 13: luxuriat vitis, Plin. 17, 22, 35, § 178.
Comp., Cic. Leg. 3, 14, 32.
Sup., Aug. Ep. 39.