Which term would best describe an unwarranted or unnecessary action?

The term "gratuitous" aptly describes an unwarranted or unnecessary action because it conveys the idea of something being done without justification or a valid reason. In many contexts, "gratuitous" is used to characterize actions or remarks that are excessive or superfluous, often implying that they are unwelcome or inappropriate in a given situation. This aligns perfectly with the concept of being unnecessary, as it suggests that the action does not contribute meaningfully to the situation at hand.

In contrast, the other terms connote a sense of necessity. "Required" signifies something that is needed; "essential" refers to something fundamentally important; and "indispensable" denotes something that is absolutely necessary. Thus, these options do not capture the essence of unwarranted actions, making "gratuitous" the most suitable choice to describe an action that lacks justification.