Which word describes someone who is tireless or seemingly tireless?

The word that describes someone who is tireless or seemingly tireless is "indefatigable." This term is often used to characterize individuals who persist relentlessly in their efforts, showing no signs of fatigue or weariness. An indefatigable person is one who can continue working or striving without giving in to exhaustion, exhibiting great stamina and perseverance in various situations, be it in work or personal endeavors.

This quality is particularly admired in contexts where determination and resilience are crucial. The use of "indefatigable" conveys a strong sense of energy and commitment, emphasizing the individual's ability to maintain a high level of activity and enthusiasm over an extended period, which is often considered inspirational and highly commendable.

Other options, while valid words, describe different qualities: "lackadaisical" refers to a lack of interest or enthusiasm, "inveterate" describes long-established habits that are unlikely to change, and "libertine" pertains to someone who behaves without moral restraint, especially in terms of sexual behavior. None of these accurately convey the sense of tirelessness or unwavering energy that "indefatigable" does.