Which word means burdensome?

The term "onerous" is used to describe something that is burdensome or weighs heavily on someone, often implying that it involves a significant amount of effort or responsibility that is difficult to bear. It typically relates to tasks or duties that are not only challenging but also impose a considerable strain. This perfectly aligns with the meaning of burdensome.

In contrast, the other options do not convey this meaning. "Timid" refers to a lack of courage or confidence, which is unrelated to the concept of burden. "Gentle" describes something that is mild or soft in nature, while "leisurely" pertains to a relaxed or unhurried pace. Neither of these alternatives expresses the heaviness or difficulty implied by "onerous." Therefore, "onerous" is indeed the word that carries the meaning of burdensome most accurately.