All 3 Uses of

pernicious
in
The Magic Mountain

Would you allow me"—and here Herr Settembrini bent forward on his chair, and with a smile he placed both feet on the floor, tucked his folded hands between his knees, and thrust his head forward at a slight tilt—"would you allow me," he repeated with some emotion in his voice, "to lend you a helping hand in your exercises and experiments and to play a corrective role whenever I see danger looming in the form of some pernicious fixation?"†
Chpt 5.1

I can assure you that mankind is about to find its way back to this point of view, to recognize that the task of true science is not the pursuit of worthless information, but rather the elimination on principle of what is pernicious, even of what is merely without significance as an idea, and, in a word, to proclaim instinct, moderation, choice.†
Chpt 6.3

The Church fathers called 'mine' and 'yours' pernicious words, described private property as usurpation and thievery.†
Chpt 6.3 *

Definition:

harmful or something spreading harm -- especially in a gradual or subtle way