Ἀχαΐα

Acts 18:12 Ἀχαΐας of Achaia

While Gallio was proconsul of Achaia, the Jews coordinated an attack on Paul and brought him before the judgment seat.

Here: The Roman province of southern Greece. Its capital and the governor's seat was Corinth, so the proconsul was right there in the city where Paul was working.

Acts 18:27 Ἀχαΐαν, Achaia,

When Apollos resolved to cross over to Achaia, the brothers encouraged him and wrote to the disciples there to welcome him. On his arrival, he was a great help to those who by grace had believed.

Here: The Roman province of southern Greece, governed from Corinth. Everyone reading would think mainly of Corinth, and 19:1 confirms that is where Apollos went.

Acts 19:21 Ἀχαΐαν Achaia

After these things had happened, Paul resolved in the Spirit to go to Jerusalem, passing through Macedonia and Achaia. “After I have been there,” he said, “I must see Rome as well.”

Here: The Roman province of southern Greece. Its capital was Corinth, home of the church that 1 and 2 Corinthians were written to.

Romans 15:26 Ἀχαΐα Achaia

For Macedonia and Achaia were pleased to make a contribution for the poor among the saints in Jerusalem.

1 Corinthians 16:15 Ἀχαΐας of Achaia

You know that Stephanas and his household were the first converts in Achaia, and they have devoted themselves to the service of the saints. Now I urge you, brothers,

Here: The Roman province covering southern Greece. Corinth was its capital. It is not just the city of Corinth.

2 Corinthians 1:1 Ἀχαΐᾳ· Achaia;

Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother, To the church of God in Corinth, together with all the saints throughout Achaia:

Here: The Roman province covering southern and central Greece, with Corinth as its capital. Believers lived in places like Cenchreae (Rom 16:1) and Athens (Acts 17:34).

2 Corinthians 9:2 Ἀχαΐα Achaia

For I know your eagerness to help, and I have been boasting to the Macedonians that since last year you in Achaia were prepared to give. And your zeal has stirred most of them to do likewise.

Here: The Roman province of southern Greece, with Corinth as its capital. Paul names the province, not just the city, and so includes the believers around Corinth (compare 1:1).

2 Corinthians 11:10 Ἀχαΐας. of Achaia.

As surely as the truth of Christ is in me, this boasting of mine will not be silenced in the regions of Achaia.

Here: The Roman province of southern Greece, with Corinth as its capital. It is set against Macedonia (v. 9), whose churches Paul did accept help from.

1 Thessalonians 1:7 Ἀχαΐᾳ. Achaia.

As a result, you have become an example to all the believers in Macedonia and Achaia.

1 Thessalonians 1:8 Ἀχαΐᾳ, Achaia,

For not only did the message of the Lord ring out from you to Macedonia and Achaia, but your faith in God has gone out to every place, so that we have no need to say anything more.

Here: The Roman province of southern Greece, with its capital at Corinth, where Paul was probably writing. Together with Macedonia it means the whole Greek peninsula.