The word "goodsized" is an adjective that refers to something that is of a satisfactory or adequate size. As for its antonyms, here are some options that can convey a different meaning: undersized, tiny, minuscule, inadequate, small, insufficient, meager, limited, diminutive, paltry, and puny. These words imply that something is not big enough or lacks the necessary quantity or quality. It's also worth noting that the antonyms of "goodsized" depend on the context in which it is used. For instance, a "tiny" waist can be a desirable trait, but a "tiny" house may not be.