Not having symmetry; lacking balanced proportions or arrangement. The artist's unsymmetrical design gave the painting a unique and dynamic appearance.
Not identical on both sides of a central line; having parts that do not correspond in shape, size, or arrangement. The unsymmetrical shape of the vase made it difficult to find a suitable spot for it on the shelf.
Chemistry: describing a molecule or chemical species whose substituent groups are arranged in such a way that the whole is not symmetrical. Unsymmetrical dimethylhydrazine is used as a propellant in several rockets.