pernicious

Tending to cause death or serious injury; deadly.

Causing great harm; destructive.

Quick.

Having the property of destroying or being injurious; hurtful; destructive.

Wicked; malicious; evil-hearted.

Quick; swift (to burn).

Having the quality of injuring or killing; destructive; very mischievous; baleful; malicious; wicked.

Causing much harm in a subtle way.

Causing death or injury; deadly.

exceedingly harmful