WordNet (r) 3.0 (2006):

Gaius
    n 1: Roman Emperor who succeeded Tiberius and whose uncontrolled
         passions resulted in manifest insanity; noted for his
         cruelty and tyranny; was assassinated (12-41) [syn:
         Caligula, Gaius, Gaius Caesar]

Easton's 1897 Bible Dictionary:

Gaius
   (1.) A Macedonian, Paul's fellow-traveller, and his host at
   Corinth when he wrote his Epistle to the Romans (16:23). He with
   his household were baptized by Paul (1 Cor. 1:14). During a
   heathen outbreak against Paul at Ephesus the mob seized Gaius
   and Aristarchus because they could not find Paul, and rushed
   with them into the theatre. Some have identified this Gaius with
   No. (2).

     (2.) A man of Derbe who accompanied Paul into Asia on his last
   journey to Jerusalem

     (3.) A Christain of Asia Minor to whom John addressed his
   third epistle (3 John 1:1).


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

Gaius, lord; an earthly man