The term POWERFUL SPEAKER can be summarized as a Stentor, which is a seven-letter word. A Stentor was a figure in Greek mythology who had a loud and powerful voice. He was a herald of the Greek army in the Trojan War and was known for his ability to speak with great volume and clarity. In modern times, a Stentor is used to refer to someone who has a strong and powerful voice, often used in public speaking or broadcasting.