There are several synonyms for the word "rotundness" including plumpness, roundness, portliness, and corpulence. These words all share a similar meaning of being round or full in shape, generally implying a larger size or weight. While some may view rotundness in a negative light, these synonyms offer a variety of ways to describe this physical characteristic in a more neutral or positive way. Additionally, the use of synonyms can help to diversify one's vocabulary and prevent repetition in writing or conversation.