Pronounced ju (third tone) and gu (third tone) in "Tang Yun" and "Zheng Yun" respectively, same pronunciation as "gong". Pronounced gu (third tone) in "Jiyun", same pronunciation as "gong". Explained in "Shuowen Jiezi" as stones by the water. Also pronounced qu (second tone) in "Jiyun", same pronunciation as "qiong". Same meaning.