There’s one usage of the word “ἐκκλησία” that people have used to argue it simply means “a gathering”. Its in Acts 19, where the people of Ephesus riot because Paul’s preaching has affected the idol-maker’s income.
When they heard this […that Paul says that gods made by human hands are no gods at all], they were furious and began shouting: “Great is Artemis of the Ephesians!” Soon the whole city was in an uproar…
Paul wanted to appear before the crowd (δῆμον), but the disciples would not let him…
The assembly (ἐκκλησία) was in confusion: Some were shouting one thing, some another. Most of the people did not even know why they were there…
The city clerk quieted the crowd and said: “Fellow Ephesians,… you ought to calm down and not do anything rash… If, then, Demetrius and his fellow craftsmen have a grievance against anybody, the courts are open and there are proconsuls. They can press charges. If there is anything further you want to bring up, it must be settled in a legal assembly (ἐκκλησίᾳ). As it is, we are in danger of being charged with rioting because of what happened today. In that case we would not be able to account for this commotion, since there is no reason for it.”
After he had said this, he dismissed the assembly (ἐκκλησίαν).
Does ἐκκλησία here mean “crowd”? Luke uses the normal word for crowd earlier, so why start using the word ἐκκλησία?
It’s because the word isn’t a Christian word… nor is it a religious word… its a secular word. “In classical Greek, the term was used almost exclusively for political gatherings. In particular, in Athens the word signified the assembling of the citizens for the purpose of conducting the affairs of the polis” (“Church”, BEDBT).
The whole issue in Acts 19 is that an army of people appear, people with a purpose and an ideology, but they’re not a legal one. They’re acting like a ἐκκλησίαν, but they’re doing it wrong.
Acts 19 doesn’t prove ἐκκλησία means “crowd” or “generic gathering”, it just proves that Demetrius the silversmith was an idiot who almost got arrested for calling an ἐκκλησία (town meeting) without authority to do so.