pernicieux

Borrowed from Latin perniciōsus.

• IPA^(key): /pɛʁ.ni.sjø/

pernicieux (feminine 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, translated by Stephen William White:

   • 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!

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, translated 1768 by John Hawkesworth:

     [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!

• “pernicieux”, in Trésor de la langue française informatisé [Digitized Treasury of the French Language], 2012.