Synonyms of pernicious

Adjective

1. baneful, deadly, pernicious, pestilent, noxious (vs. innocuous)

usage: exceedingly harmful

2. insidious, pernicious, subtle, harmful (vs. harmless)

usage: working or spreading in a hidden and usually injurious way; "glaucoma is an insidious disease"; "a subtle poison"

Definition and meaning of pernicious (Dictionary)