Of an action or its result: excessively injurious or cruel; of the nature of a gross violation of justice, morality, decency, etc.; wicked, evil…

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

As an intensive, qualifying a word denoting something in itself bad, irksome, or undesirable: Grievous… of injury, loss, disease, etc. Obsolete.

Originally (of a disease): potentially fatal; extremely severe; exceptionally contagious or infectious; incurable. Now chiefly (of a neoplasm)…