From the Webster online dictionary. Interesting.
1: 1. The derivation of the word is generally said to be from the Greek kuriakon (kuriakon) "belonging to the Lord." But the derivation has been too hastily assumed. It is probably connected with kirk, the Latin circus, circulus, the Greek kuklos (kuklos) because the congregations were gathered in circles. 2. Ecclesia (ekklesia) the Greek word for church, originally meant an assembly called out by the magistrate, or by legitimate authority. It was in this last sense that the word was adapted and applied by the writers of the New Testament to the Christian congregation. In the one Gospel of St. Matthew the church is spoken of no less than thirty-six times as "the kingdom." Other descriptions or titles are hardly found in the evangelists. It is Christ�s household, (Matthew 10:25) the salt and light of the world, (Matthew 5:13,15) Christ�s flock, (Matthew 26:31; John 10:15) its members are the branches growing on Christ the Vine, John 15; but the general description of it, not metaphorical but direct, is that it is a kingdom, (Matthew 16:19) From the Gospel then we learn that Christ was about to establish his heavenly kingdom on earth, which was to be the substitute for the Jewish Church and kingdom, now doomed to destruction (Matthew 21:43) The day of Pentecost is the birthday of the Christian church. Before they had been individual followers Jesus; now they became his mystical body, animated by his spirit. On the evening of the day of Pentecost, the 3140 members of which the Church consisted were -- (1) Apostles; (2) previous Disciples; (3) Converts. In (Acts 2:41) we have indirectly exhibited the essential conditions of church communion. They are (1) Baptism, baptism implying on the part of the recipient repentance and faith; (2) Apostolic Doctrine; (3) Fellowship with the Apostles; (4) The Lord�s Supper; (5) Public Worship. The real Church consists of all who belong to the Lord Jesus Christ as his disciples, and are one in love, in character, in hope, in Christ as the head of all, though as the body of Christ it consists of many parts. (references)