Final answer:
The term to make something less intense or severe is 'mitigate.' It is often used to describe the reduction of severity in various contexts such as medicine, politics, or language.
Step-by-step explanation:
The term used to describe the action of making something less intense or severe, to soften or diminish, is mitigate. The other options provided do not align with this definition. Malevolent means having or showing a wish to do evil to others, maniacal indicates characterized by madness; insane, and magnanimous is showing or suggesting a lofty and courageous spirit. The word mitigate is commonly used to convey the idea of reducing the severity, seriousness, or painfulness of something. An example of this in political terms could be the process of détente, which refers to the lessening of tensions between adversaries. Additionally, in literature, authors might use euphemisms to mitigate the harshness of language when referring to unpleasant or embarrassing situations, which aligns with the provided context of the lady Madeline's condition in the given text. Her physicians could not alleviate the severity of her illness.