Easton's Bible Dictionary (1897)
Prince, a Greek rhetorician, in whose “school” at Ephesus Paul disputed daily for the space of two years with those who came to him (Acts 19:9). Some have supposed that he was a Jew, and that his “school” was a private synagogue.
Smith's Bible Dictionary (1863)
(sovereign), the name of a man in whose school or place of audience Paul taught the gospel for two years, during his sojourn at Ephesus. ) The presumption is that Tyrannus himself was a Greek, and a public teacher of philosophy or rhetoric.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
TYRAN'NUS (tyrant), the name of the Greek rhetorician of Ephesus in whose lecture-room Paul delivered discourses daily for two years. Acts 19:9. Paul and he must have occupied the same room at different hours. He may have been a convert.
Hitchcock's Bible Names (1869)
a prince; one that reigns