"Rakusaku" comes from the Classical Chinese word "luosuo" (落索 "wither, shrivel; fall low, fall on hard times; lonely, lonesome"). Thus, the title blends "raku" (落 "fall; drop") meaning words "dropped" (overlooked, missed) by other Japanese dictionaries plus "yōshū" (葉集, or "hashū" in "on"-reading) abbreviating "Irohashū" (色葉集 ""iroha" collection") meaning a dictionary collated in "iroha" order (e.g., the 12th-century "Iroha Jiruishō"). Despite the compiler's intention of including overlooked words, Bailey discovered that more than half of the "Rakuyōshū" entries are found in contemporary Japanese dictionaries, primarily 15th-century "Setsuyōshū" editions, and many others occur in Chinese rime dictionaries.