Shōshin Nagamine was a Japanese author from Okinawa as well as a soldier, police officer, and karate master. He wrote two books, The Essence of Okinawan Karate-Do and Tales of Okinawa's Great Masters. Both have been translated into English.
Although his style is not Gojuryu, the Essence of Okinawan Karate-Do contains plenty of interesting and useful background, insights and terminology. The Table of Contents alone makes for a highly informative glossary.