'又大又圆' is a fixed four-character pattern used to describe something that simultaneously possesses two positive physical qualities: large size and perfect roundness. It follows the grammatical structure '又 + Adjective 1 + 又 + Adjective 2', which emphasizes both attributes equally and often conveys admiration, vivid imagery, or natural harmony. The word functions adjectivally—typically modifying nouns like fruits, moons, eyes, or animal features—and appears frequently in descriptive writing, children’s literature, and everyday speech when highlighting pleasing, symmetrical shapes.

This phrase carries a warm, slightly poetic tone and is especially common when describing natural or wholesome things—such as full moons, ripe fruits (like watermelons or pomelos), or the eyes of certain animals (e.g., pandas or puppies). Unlike standalone adjectives, it cannot be modified by degree adverbs like 'very' (很) and rarely takes aspect particles (了, 过). Its rhythm and repetition make it memorable and child-friendly, reinforcing its frequent use in storytelling and early language learning.