The term 'board medium' can refer to a variety of different things. RADIO (5 letters) is a form of communication that uses electromagnetic waves to transmit sound, such as music or speech. AGAR (4 letters) is a type of gelatinous substance derived from algae, which is often used in scientific experiments. ORACLE (6 letters) is a person or thing that is believed to provide wise and insightful counsel. Oils (4 letters) are substances that are composed of hydrocarbons and are typically liquid at room temperature. All of these items can be used as board mediums in various ways.