Full of malign, deadly, or noxious influence; pernicious, destructive, noxious, injurious, mischievous, malignant. Physically or generally.

Baleful, fraught with evil.

Of things, events, accidents, etc.: Bringing serious trouble or discomfort; having injurious effects; †causing hurt or pain. (Now only with mixture…

Of a thing: evil in nature and effects; baleful, gravely injurious. Of sin: †heinous (obsolete).

Malignant, virulent, harmful. Obsolete.

Venomous; virulent, malignant, spiteful. Obsolete exc. dialect.

Medicine. Of diseases, etc.: Characterized by extreme malignancy or violence.

Evil in nature and effects; baleful, harmful, gravely injurious. Formerly also of material substances, plants, etc.: †poisonous, deleterious (obsolete…

That blasts, in various senses of the verb; blighting, striking with baleful effect, defaming, etc.

The hyperbolical use of the word in sense 6 gives rise to a weakened sense: Causing serious harm, disastrous, gravely mischievous.

That blights; blasting, withering.

figurative and in extended use: irreversible, irreparable; extremely severe; calamitous, disastrous.