See Definition for synagoge { [G4864]}
See Definition for ekklesia { [G1577]}
See Definition for panegyris { [G3831]}
According to their derivation, synagoge is simply an assembly,
a mass of people gathered together?
ekklesia is a narrower word, also an assembly, but including
only those specially called together out of a larger multitude,
for the transaction of business. ekklesia usually denotes a
somewhat more select company than synagoge. A significant use of
ekklesia in strict harmony with its derivation was common among
the Greeks. It was their common word for the lawful assembly in a free
Greek city of all those possessing the rights of citizenship, for the
transaction of public affairs. They were summoned out of the
whole population, ``a select portion of it, including neither the
populace, nor strangers, nor yet those who had forfeited their civic
rights''(Trench). synagoge had been, before N.T. times,
appropriated to designate a synagogue, a Jewish assembly for worship,
distinct from the Temple, in which sense it is used in the N.T.
Probably for that reason, and also for its greater inherent
etymological fitness, ekklesia is the word taken to designate
a Christian church, a company of believers who meet for worship.
Both these words, however, are sometimes used in the N.T. in a
non-technical sense.
panegyris, occurring only in Heb 12:23, differs from both,
denoting a solemn assembly for festal rejoicing.