PERNICIOUSLY
banefully, perniciously
(adverb) in a noxiously baneful way; “this banefully poisoned climate”
insidiously, perniciously
(adverb) in a harmfully insidious manner; “these drugs act insidiously”
Source: WordNet® 3.1
Etymology
Adverb
perniciously (comparative more perniciously, superlative most perniciously)
In a pernicious manner.
Source: Wiktionary
PERNICIOUS
Per*ni"cious, a. Etym: [L. pernix, -icis.]
Definition: Quick; swift (to burn). [R.] Milton.
Per*ni"cious, a. Etym: [L. perniciosus, from pernicies destruction,
from pernecare to kill or slay outright; per + necare to kill, slay:
cf. F. pernicieux. Cf. Nuisance, Necromancy.]
Definition: Having the quality of injuring or killing; destructive; very
mischievous; baleful; malicious; wicked.
Let this pernicious hour Stand aye accursed in the calendar. Shak.
Pernicious to his health. Prescott.
Syn.
– Destructive; ruinous; deadly; noxious; injurious; baneful;
deleterious; hurtful; mischievous.
– Per*ni"cious*ly, adv., -- Per*ni"cious*ness, n.
Source: Webster’s Unabridged Dictionary 1913 Edition