Antonyms for the word "urn-shaped" could include a variety of descriptive terms. Instead of urn-shaped, an object might be round, flat, square, triangular, or irregularly shaped. It might also be tall, short, wide, or narrow, depending on its dimensions. In terms of style, an object might be modern, minimalist, ornate, rustic, or classic, among many other possibilities. The opposite of an urn-shaped object might also be something that serves a different purpose, such as a vase, bowl, basket, or sculpture. Whatever the antonym might be, it would serve to provide a contrasting description to something that is shaped like an urn.