Which term is associated with a noticeable lack of energy or interest?

The term that signifies a noticeable lack of energy or interest is "lassitude." Lassitude describes a state of physical or mental weariness, suggesting fatigue or a lack of motivation rather than simple indifference. When someone is experiencing lassitude, they might feel drained, both physically and emotionally, which can lead to a disinterest in activities that would normally engage them.

The other options reflect different states or attitudes. Enthusiasm denotes a strong excitement or eagerness, which is the opposite of lacking energy or interest. Indifference expresses a lack of concern or interest, but it does not specifically indicate the weariness associated with lassitude. Zeal represents intense passion or eagerness in pursuits, which again contrasts with the sense of fatigue inherent in lassitude. Thus, lassitude is the most accurate descriptor of a significant absence of energy or interest.