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pernicious

/pərˈnɪʃəs/

Causing harm in a subtle, destructive way.

From Latin per (through) + Latin nex / necis (violent death).

adjective
per
PIE
Verified
*per-
reconstructed
forward; through; before; toward

from Old French pernicios (13c., Modern French pernicieux ) and directly

+1 more source
Latin
Verified
per
through, by means of, completely

from Old French pernicios (13c., Modern French pernicieux ) and directly

+1 more source
Old French
Verified
pernicios
borrowed into French as an adjective meaning destructive

from Old French pernicios (13c., Modern French pernicieux ) and directly

+1 more source
nex / necis
Latin
AI-inferred
nex, necis
violent death, slaughter
Latin
AI-inferred
perniciēs
destruction, ruin; formed with per + necis
Combined
perniciēs / perniciosus
Latin combined 'through/completely' + 'death, slaughter' into 'destruction'; the adjective perniciosus became Old French pernicios and then English pernicious.
Old French
Verified
pernicios
13th-century French adjective

from Old French pernicios (13c., Modern French pernicieux ) and directly

+1 more source
Middle English
AI-inferred
pernicious
early 15th-century borrowing
Modern English
pernicious

This is one of those words that sounds like it ought to wear a black cloak. In Latin, it was built from per, “through” or “completely,” plus nex, “slaughter” — so the original idea was destruction that runs all the way through something, not just a bruise on the surface. That’s why it sits in the same family as innocent, noxious, and nocent: all those words are playing on the old Latin idea of harm, injury, and death. English picked it up through Old French pernicios in the 13th century, and by the 1500s it was being used for things that didn’t just hurt you once, but worked like a slow poison. If you want to remember it, think of a harm so thorough it doesn’t merely strike — it seeps.

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