What does it mean to gradually lessen or reduce an emotion or quality?

The term that means to gradually lessen or reduce an emotion or quality is "ebb." This word is often used to describe a decrease or decline in intensity or strength, particularly in relation to emotions or particular feelings over time. For instance, when someone's enthusiasm "ebbs," it indicates that their excitement is fading away gradually rather than ceasing abruptly.

The other terms convey different meanings; for example, "intensify" refers to increasing the strength or degree of an emotion or quality. "Accentuate" means to make something more noticeable or prominent, which involves enhancement rather than reduction. Similarly, "heighten" indicates an increase in intensity or elevation of a feeling or quality, which also does not align with the idea of lessening. Thus, "ebb" is the appropriate choice as it encapsulates the concept of a gradual decrease.