Is used in the New Testament for the whole region of Greece south of Macedonia, including the Peloponnesus, or Morea, and some territory north of the gulf of Corinth, Acts 18:12; 19:21; 1 Corinthians 11:10. Achaia Proper, however, was a province of Greece, of which Corinth was the capital, and embraced the northwestern part of the Pelopennesus. See GREECE.
These dictionary topics are from American Tract Society Bible Dictionary published in 1859. Public Domain, copy freely.
Rand, W. W. "Entry for 'ACHAIA'". "American Tract Society Bible Dictionary".