WordNet (r) 3.0 (2006):

Tyrannus
    n 1: type genus of the Tyrannidae: tyrant flycatchers [syn:
         Tyrannus, genus Tyrannus]

Easton's 1897 Bible Dictionary:

Tyrannus
   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.


Hitchcock's Bible Names Dictionary (late 1800's):

Tyrannus, a prince; one that reigns