There are quite a few antonyms for the word "wellset," which means "having a firmly developed and attractive physique." Some antonyms include "weak," "scrawny," "frail," "thin," "delicate," "fragile," "insubstantial," and "skinny." These words indicate a lack of physical strength or muscle tone. Other antonyms for "wellset" would be words like "unfit," "out of shape," "flabby," "chubby," "overweight," and "obese." These words describe a body that is not toned, muscular or healthy. Using antonyms such as these can help to better describe a character or person in a story or to effectively communicate when describing someone's appearance.