Which word describes something that is burdensome or hard to endure?

The term that effectively describes something that is burdensome or hard to endure is "onerous." This word originates from the Latin term “onus,” meaning burden. It conveys the idea of something that imposes a great deal of difficulty or is heavy with responsibility. In contexts such as work, obligations, or tasks, labeling them as onerous signifies that they are not just challenging but also draining and unpleasant to work through.

In contrast, words like "lightweight," "simple," and "inconsequential" suggest ease, lack of complexity, or minimal impact. "Lightweight" implies a lack of physical or emotional weight, "simple" denotes ease of understanding or minimal effort, and "inconsequential" refers to something that is unimportant or trivial. These descriptors do not align with the idea of burdensome or hard to endure, reinforcing why "onerous" is the most appropriate choice.