Which term refers to bitterness or long-standing resentment?

The term "rancour" specifically denotes a deep-seated, longstanding bitterness or resentment that one may feel toward someone else. This word captures the emotional weight and lasting nature of such feelings, often stemming from past grievances or conflicts. It reflects a sense of animosity that can linger over time, making it a precise choice for describing situations involving prolonged hostility or ill will.

In contrast, the other options do not convey the same meaning. "Rampant" refers to something unrestrained or unchecked, "inalienable" describes rights or privileges that cannot be taken away, and "pandemic" signifies a wide-reaching disease outbreak. None of these terms relate to emotions of bitterness or resentment, highlighting the appropriateness of "rancour" as the correct answer.