Definitions for "Pernicious"
Having the quality of injuring or killing; destructive; very mischievous; baleful; malicious; wicked.
Highly injurious or destructive; deadly.
Destructive, sometimes fatal.
exceedingly harmful
adj. very harmful
working or spreading in a hidden and usually injurious way; "glaucoma is an insidious disease"; "a subtle poison"
Quick; swift (to burn).