Synonyms for Pernicious:

adj.

all (adjective)
subtle, insidious.
bad, hurtful (adjective)
fatal, deadly, damaging, pestilent, prejudicial, sinister, noxious, malignant, harmful.
dangerous (adjective)
pestilent.
evil (adjective)
sinister.
harmful (adjective)
prejudicial, fatal, sinister, malignant, risky, damaging.

n.

hazardous, perilous, disastrous, risky, unsafe. malignant, help. pernicious (noun)
harmful, pestilent, subtle, insidious, baneful, deadly, noxious.

Other synonyms:

malignant. Other relevant words:
disastrous, prejudicial, sinister, fatal, baneful, damaging, malignant.

Usage examples for pernicious

  1. Yet I can not quite agree that the habit of air- castle building is pernicious – Study of Child Life by Marion Foster Washburne
  2. " That pernicious girl is communicating with Godfrey," he said to himself, " which I particularly wish to prevent." – Love Eternal by H. Rider Haggard
  3. I tell you at once that I consider Miss Blake a most pernicious young woman, and as your father I can only express the hope that you do not intend to allow her to re- assert her evil influence over you. – Love Eternal by H. Rider Haggard