Webster's Revised Unabridged Dictionary · 1913

Pernicious

Pernicious , adjective

[Latin pernix, -icis.]

Quick; swift (to burn). [Rare] — Milton

Pernicious , adjective

[Latin perniciosus, from pernicies destruction, from pernecare to kill or slay outright; per + necare to kill, slay: compare French pernicieux. Compare Nuisance, Necromancy.]

Having the quality of injuring or killing; destructive; very mischievous; baleful; malicious; wicked.
Let this pernicious hour Stand aye accursed in the calendar. — Shakespeare
Pernicious to his health. — Prescott