圆 yuán — circle; round; circular; spherical; (of the moon) full; unit of Chinese currency (Yuan)
中秋节的月亮又大又圆。Zhōng qiū jié de yuè liang yòu dà yòu yuán.The moon at the Mid-Autumn Festival is big and round.
Common words: 圆满 (yuán mǎn)、团圆 (tuán yuán)、椭圆 (tuǒ yuán)