 Lu Erkui's (1915) "Ciyuan" (辭源 "Sources of Words") was a groundbreaking effort in Chinese lexicography and can be considered the first "cidian" "word dictionary".Shu Xincheng's (1936) "Cihai" (辭海 "Sea of Words") was a comprehensive dictionary of characters and expressions, and provided near-encyclopedic coverage in fields like science, philosophy, history.The "Cihai" remains a popular dictionary and has been frequently revised.