Synonyms of pernicious

1 Syllable
cruel
2 Syllables
crueler, deadliest, fatal, deadlier, wreckful, septic, cruelest, toxic, ruinous, harmful, noxious, evil, lethal, nocent, maligns, miasmic, wicked, deadly, mortal, malign, killing, dickens, hurtful
3 Syllables
baleful, corrupting, malefic, injurious, necrotic, mischievous, malicious, tumbledown, toxicant, damaging, blackhearted, venomous, rascally, oppugnant, poisonous, dangerous, pestilent, malignant, noisome, baneful, sinister, miasmatic, virulent, nefarious, maligning
4 Syllables
lethiferous, devastating, insalubrious, pestiferous, pestilential, ill-behaved, malevolent, prejudicial, detrimental, deleterious, ill-disposed, unnutritious, maleficent, inimical, destructive, offensive, iniquitous, calamitous, mephitical, bad-natured, prejudicious
5 Syllables
extirpative, unconducive, unwholesome, insalutary
6 Syllables
annihilative, eradicative