Which term means lacking energy or vitality?

The term that means lacking energy or vitality is "sluggish." This word specifically describes a state of reduced energy or an inclination towards inactivity, which aligns perfectly with the concept of vitality and liveliness. When something or someone is termed sluggish, it indicates a slower pace, often associated with lethargy or tiredness, thus conveying a clear absence of energetic motivation or spirited activity.

In contrast, "vigorous," "exuberant," and "dynamic" all carry positive connotations of energy and vitality. They describe states of high activity, enthusiasm, and liveliness, which are the opposite of being sluggish. "Vigorous" denotes strength and energy, "exuberant" refers to an energetic and lively expression, and "dynamic" highlights activity and progressiveness. Therefore, these terms cannot be used to describe a lack of energy or vitality, solidifying "sluggish" as the correct choice in this context.