Paul wrote several letters to the church at Thessalonica. The ancient Greek word
"Θεσσαλονίκη" ≈ "Thessalonica" comes from two Greek words.
The ancient Greek word "Θεσσᾰλός" ≈ "Thessalos", a name given to the daughter of Phillip II (father of Alexander the Great) after his victory in Thessaly - a region in northern Greece.
The ancient Greek word "νική" ≈ "victory". Later, the city was named after her for the victory there.