Gaius. Common Roman name. May be the same as in Acts 19:29, or of Derbe, Acts 20:4, but almost certainly Gaius of 1 Corinthians 1:14. The Gaius of 3 John 1:1, evidently. man of position, is probably another person.
Erastus. Perhaps the same as in 2 Timothy 4:20. The name,. Greek one, occurs: Acts 19:22.
chamberlain. treasurer. Greek. oikonomos. Occurs ten times, rendered "steward" in eight. See Luke 12:42.
Quartus. Only here. Roman name.
a brother. the brother (in Christ, Romans 16:7).