Definition of "pernicious" in English

adjective

1. Causing much harm in a subtle way.

   • pernicious influence
   • pernicious effects
   • They warned of the pernicious effects of misinformation.
   • The weed has a pernicious influence on local crops.

2. Causing death or injury; deadly.

3. (of a person) Insidiously villainous: intending to cause harm, especially in a subtle way.

adjective

1. (obsolete) swift; celeritous.