18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.

19 And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.

ἐκκλησία

Transliteration ekklēsia 

(Key)Pronunciation ek-klay-see'-ah

NOTE:  The original word translated “church” from original manuscripts is “ekklesia.” This word is the Greek word kaleo (to call), with the prefix ek (out). 

 KJV translates Strong's G1577 in the following manner: church (115x), assembly (3x).

Outline of Biblical Usage

1. a gathering of citizens called out from their homes into some public place, an assembly
   
   1. an assembly of the people convened at the public place of the council for the purpose of deliberating
   2. the assembly of the Israelites
   3. any gathering or throng of men assembled by chance, tumultuously
   4. in a Christian sense
      
      1. an assembly of Christians gathered for worship in a religious meeting
      2. a company of Christian, or of those who, hoping for eternal salvation through Jesus Christ, observe their own religious rites, hold their own religious meetings, and manage their own affairs, according to regulations prescribed for the body for order's sake
      3. those who anywhere, in a city, village, constitute such a company and are united into one body
      4. the whole body of Christians scattered throughout the earth
      5. the assembly of faithful Christians already dead and received into heaven

Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching. 

 2Th 2:1Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together G1997 unto him, 

Transliterationepisynagōgē (Key)Pronunciation ep-ee-soon-ag-o-gay' gathering together (1x), assembling together (1x).Outline of Biblical Usage [?]

1. a gathering together in one place
2. the (religious) assembly (of Christians)

Strong’s Definitions [?](Strong’s Definitions Legend)ἐπισυναγωγή episynagōgḗ, ep-ee-soon-ag-o-gay'; from G1996; a complete collection; especially a Christian meeting (for worship):—assembling (gathering) together.
a. a gathering together in one place, equivalent to τὸ ἐπισυνάγεσθαι (2 Macc. 2:7): ἐπί τινα, to one, 2 Thessalonians 2:1.
b. (the religious) assembly (of Christians): Hebrews 10:25. 

Eph. 4:16

 From whom the whole body fitly joined together and compacted by that which every joint supplieth, according to the effectual working in the measure of every part, maketh increase of the body unto the edifying of itself in love.  

Synarmologeō 

 soon-ar-mol-og-eh'-o 

fitly joined together

g4883

 soon-ar-mol-og-eh'-o; from G4862 and a derivative of a compound of G719 and G3004 (in its original sense of laying); to render close-jointed together, i.e. organize compactly:—be fitly framed (joined) together. 

 If therefore the whole church be come together into one place, and all speak with tongues, and there come in those that are unlearned, or unbelievers, will they not say that ye are mad? 

synerchomai (Key)

Pronunciation
soon-er'-khom-ahee

1. to come together, to assemble
   1. of conjugal cohabitation
2. to go (depart) or come with one, to accompany one

Mat 1:18

Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, G4905 she was found with child of the Holy Ghost. 

According to Revelation 1:11, on the Greek island of Patmos, Jesus Christ instructs John of Patmos to: "Write on a scroll what you see and send it to the seven Churches: to Ephesus, and to Smyrna, and to Pergamum, and to Thyatira, and to Sardis, and to Philadelphia, and to Laodicea."

MORE 

One of the classes taught at Westminster Seminary California is titled "Ancient Church." It covers the history of the church after New Testament times until the Medieval period. 

According to  Dr. Van Ee who has taught language and biblical studies courses at Westminster Seminary California;  

Now some might disagree, arguing that we don't find the word church in the Old Testament, and they would be correct but only for the English. The Greek word that is translated as church is ekklēsia and is used in the New Testament for a specific gathering of Christians, or for all believers together. The same word, ekklēsia, is used in the Greek translation of the Old Testament, the Septuagint, to translate the Hebrew term qāhāl, "assembly." It is used for Israel as they gathered together to appear before God or as a general reference to all of Israel. Another Greek word used to translate qāhāl is sunagōgē. It is also used to translate another word for Israel: 'ēdâ, "congregation." In the New Testament sunagōgē is most often used of a synagogue or its members, but is used for a gathering of Christians in James 2:2. The terms used in the New Testament for the church are not new ones but are rooted in the Old Testament. Thus, in at least some sense, Israel really was the Old Testament church-assembly-congregation!

And yet, we could say that the church stretches back further, even before Israel. The church includes Abraham who was summoned out of the nations (Gen 12:1), the line of Seth who called upon the name of the Lord (Gen 4:26), and Adam and Eve who embraced God's first gospel message (Gen 3:15). The church could even include Adam and Eve as created in perfection to dwell in God's presence