What term describes an attitude that is characterized by a lack of spirit or interest?

The term that best describes an attitude characterized by a lack of spirit or interest is "slackadaisical." This word conveys a sense of carelessness or a lazy approach to tasks or responsibilities, suggesting an absence of enthusiasm and energy. It paints a vivid picture of someone who is not only uninterested but also lacking in motivation, making it the most suitable choice in this context.

While the other options also suggest varying degrees of disinterest or lack of enthusiasm, they do so in slightly different ways. "Indifferent" denotes a lack of concern, but it doesn't explicitly convey laziness. "Listless" can describe someone lacking energy or vitality, which may align closely with a lack of spirit but does not imply a casual or careless attitude. "Unenthusiastic" simply communicates a lack of enthusiasm, but again, it doesn’t capture the same connotation of a careless approach to life or responsibilities that "slackadaisical" does.