To "inure" means to:

The term "inure" refers to the process of becoming accustomed to something, often something unpleasant or undesirable. When a person is inured to a particular condition or circumstance, it implies they have developed a tolerance or acceptance towards it, usually after repeated exposure. This understanding aligns perfectly with the notion of habituating to something that may not be favorable but has become a part of their experience over time.

In the context of the options presented, this definition directly supports the choice of habituating to something undesirable, distinguishing it from the others, which focus on different meanings and concepts not related to the sense of acclimatization or adaptation in a negative context.