Tyrannus in Fausset's Bible Dictionary

Acts 19:9. In whose school at Ephesus Paul discussed (dielegeto, "reasoned"; same Greek, Acts 17:2) gospel truths with disciples and inquirers (having withdrawn from cavilers) daily for two years. A private synagogue (called beet midrash by the Jews), or rather the hall of a Gentile sophist or lecturer on rhetoric and philosophy; his name is Greek, and the "one" prefixed implies that there was no definite leaning to Christianity in him. He probably hired out his school when not using it himself. Paul in leaving the synagogue would be likely to take a Gentile's hall to gain access to the Gentiles.