What term describes someone marked by arduous effort in their work?

The term that best describes someone marked by arduous effort in their work is "diligent." This word conveys a strong sense of hard work, persistence, and careful attention to detail. Diligence involves a commitment to completing tasks thoroughly and consistently, which aligns perfectly with the idea of putting in significant effort to achieve results.

The other terms do not relate to the idea of hard work or effort. "Disallow" means to refuse or reject something, while "disparage" refers to speaking about someone or something in a way that suggests they are of little worth. Similarly, "derogate" means to detract from or belittle someone or something. None of these terms capture the essence of dedication and effort represented by "diligent."