pernicieux

Borrowed from Latin perniciōsus.

• IPA^(key): /pɛʁ.ni.sjø/

pernicieux (feminine singular pernicieuse, masculine plural pernicieux, feminine plural pernicieuses)

1. (medicine, rare) Insidious. Having a slow and discreet, but dangerous evolution.
   • Anémie pernicieuse: pernicious anemia, or Biermer's anemia, a form of megaloblastic anemia due to vitamin B12 deficiency.
   • Fièvre pernicieuse: pernicious fever. Old term for neuro-malaria, the most serious form of malaria fever.
     • 1879, Jules Verne, L'Île mystérieuse, Part 3, Chapter 10,

     Elle est insuffisante, répondit le reporter, et un troisième accès de fièvre pernicieuse qu’on ne coupe pas au moyen de la quinine est toujours mortel!

     [It] Is insufficient. And a third attack of pernicious fever, when one cannot break it by means of quinine, is always mortal! (1876, tranlator Stephen William White)

2. (literary) Morally harmful; pernicious.
   • 1715, Alain-René Lesage, Histoire de Gil Blas de Santillane, Book II, Chapter VII,

     Va, je t’abandonne aux gens qui te donnent de si pernicieux conseils.

     Go, I shall let you to those who give you such pernicious advice.

3. (dated) Literally harmful or dangerous, usually of animals or persons.
   • 1699, François Fénelon, Les Aventures de Télémaque, Book 6,

     [S]ors aussi, pernicieux enfant: tu m'as fait plus de mal que lui!

     Depart thou also, pernicious boy! for my misfortunes are derived rather from thee than from him! (1768, John Hawkesworth translator)

• “pernicieux” in le Trésor de la langue française informatisé (The Digitized Treasury of the French Language).