What describes a person who lacks enthusiasm or energy?

The term that describes a person who lacks enthusiasm or energy is "lethargic." This word specifically refers to a state of sluggishness, inactivity, or a lack of energy and alertness. When someone is lethargic, they often feel drowsy or indifferent, which conveys the absence of enthusiasm.

In contrast, "ebullient" describes someone who is bubbly, enthusiastic, and energetic—essentially the opposite of lacking energy. "Pallid" typically refers to something that is pale or lacking color, often used to describe a person's complexion rather than their energy levels. "Prolific" refers to someone or something that produces a lot of work or results, particularly in terms of creativity or output, which does not pertain to energy or enthusiasm levels.