[{"Bold_text": "noun", "List Items": ["a person who is devoted to one subject or to one particular branch of a subject or pursuit.", "a medical practitioner who devotes attention to a particular class of diseases, patients, etc.", "U.S. Army.an enlisted person of one of four grades having technical or administrative duties, the grades corresponding to those of corporal through sergeant first class but not requiring the exercise of command.", "Stock Exchange.a member of an exchange who buys and sells a single stock or a particular group of stocks in their own name or for other stockbrokers and thus helps maintain the market in those securities on that exchange."]}]