What describes someone who is filled with enthusiastic devotion to a principle or cause?

The term that describes someone who is filled with enthusiastic devotion to a principle or cause is zealous. A zealous individual exhibits a strong passion and fervor for their beliefs or causes, often demonstrating a commitment that goes beyond mere interest. This type of person actively supports and promotes their convictions, displaying energy and enthusiasm that characterizes their approach to advocacy.

In contrast, the other options denote varying degrees of lack of passion or commitment. Indifferent refers to a lack of interest, enthusiasm, or concern regarding a cause. Dispassionate suggests a cool or rational attitude devoid of strong feelings or emotional engagement, while neutral implies an absence of bias or involvement, often indicating a decision not to take a side in a debate or cause. These terms collectively highlight the absence of the enthusiastic devotion that is intrinsic to being zealous.