1) possessing the same citizenship with others, a fellow citizen
1a) of Gentiles as received into communion of the saints
1b) of the people consecrated to God
Part of Speech: noun masculine
From G4862 and G4177; a native of the same town, that is, (figuratively) co-religionist (fellow Christian): - fellow-citizen.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root συμπολίτης; click on the second column to search for that grammatical form of the root συμπολίτης; click on the third column to search for that word and grammatical form; click on the total to search for the root συμπολίτης.