Allantoid is a term that refers to an egg-shaped structure found in certain organisms. Some synonyms for allantoid include ovoid, egg-shaped, ellipsoid, and oblong. These words all describe a shape that is similar to an egg, with a slightly elongated or curved form. Other possible synonyms might include rounded, bulbous, or even potato-shaped, depending on the specific characteristics of the structure in question. By using these different synonyms, writers can add variety and depth to their descriptions, helping readers to imagine and understand the shape and form of the allantoid structure.