What is the primary characteristic of something described as rotund?

The term "rotund" is primarily used to describe something that is rounded or plump in shape. It often refers to objects or beings that have a full, rounded form. This characteristic can apply to various contexts, such as physical appearance, shapes of objects, or even sounds that are rich and full.

In contrast, the other choices represent different attributes that do not convey the essence of the word rotund. Being sharp or keen relates more to precision or acuteness, which is not applicable here. Aplomb refers to a sense of confidence or composure, while a scornful attitude denotes disdain or contempt. None of these attributes align with the primary meaning of rotund, making the choice of being rounded or plump the most fitting description.