In reading more about ostracism, I encountered the word
"proxeny". I haven't yet found the definition, but here's the quote:
"Theopompos in the Tenth Book of the Philippika says about Kimon: 'When five years had not yet gone by, a war having broken out with the Lacedaemonians, the People sent for Kimon, thinking that by his proxeny he would make the quickest peace. When he arrived at the City, he ended the war."
I'm guessing it means his friends among the enemy.

I found this:
"There was an institution -particularly in Greece- that introduced this private pact between strangers into the public domain: proxeny.
Proxenia was a contract between a State and the citizen of a polis. The latter, chosen among the most influential and wealthy personalities of his city, was a sort of godfather of a foreign State and its citizens. He would welcome, at his own expense, the travellers or the ambassadors who would arrive from the other country; he would sponsor them and represent them in the circumstances of religious ceremonies and commercial intercourses. In exchange, he would benefit of honours and privileges, mostly symbolical, from the nation with which he would have signed the pact.