Thayer's Greek Lexicon

 1. prayer addressed to God
2. a place set apart or suited for the offering of prayer
  1) a synagogue
  2) a place in the open air where the Jews were wont to pray,
outside the cities, where they had no synagogue
2b1. such places were situated upon the bank of a stream or the
shore of a sea, where there was a supply of water for
washing the hands before prayer

For Synonyms see entry G5828