The term 'SOUND MEDIUM' can be broken down into two words, 'SOUND' and 'MEDIUM'. SOUND is a vibration that travels through the air or another MEDIUM and can be heard when it reaches a person's ear. A MEDIUM is a means of communication or transportation. In this case, the crossword solution for the term 'SOUND MEDIUM' is 'RADIO', which is a type of SOUND MEDIUM. RADIO is a form of communication that uses electromagnetic waves to transmit SOUND signals from one place to another.