Pernicious, a.
Etymology: [L. perniciosus, from pernicies destruction, from pernecare to kill or slay outright; per + necare to kill, slay: cf. F. pernicieux. Cf. 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. 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.
1 other Webster entry under this spelling
Pernicious, a.
Quick; swift (to burn). [R.] Milton.
Shades of meaning
Pernicious (L. per, through, and neco, kill) signifies having the power of destroying or injuring, tending to hurt or kill. Pernicious is stronger than injurious; that which is injurious is capable of doing harm; that which is pernicious is likely to be destructive. Noxious (L. noceo, hurt) is a stronger word than noisome, as referring to that which is injurious or destructive. Noisome now always denotes that which is extremely disagreeable or disgusting, especially to the sense of smell; as, the noisome stench proclaimed the presence of noxious gases.