The English word "church" comes from the Greek "kuriakon," the Lord's (house), so used to some extent by the early Greek Christians. (Skeat.) The Teutonic tribes, when converted to Christianity, adopted this Greek word for the house of worship, and it is found now in the German "kirche," the Scottish "kirk," Anglo-Saxon "cyrice," "cirice," "circe," from which comes the English "church."
The use of the word was gradually extended to the assembly meeting at the church, an extension similar though in the opposite direction, to that which has taken place in the words synagogue, parish, school, etc. Those who wish to avoid the confusion which arises from applying the same word to the building and the assembly, would be keeping nearer to the "history," at least, if they applied the term "church" only to the building. The Greek Christians themselves are not known to have ever used "kuriakon" for the assembly, and in modern Greek "ekklesia" is the only word in both senses. From this through the Latin form "ecclesia" came the French "eglise," our word "ecclesiastical," etc.
Footnote, Matthew 18:17; Pg. 388, Commentary of the New Testament, John A. Broadus, DD, LLD; 1886. (Mr. Broadus was a Baptist.)