The word "church" comes from the Latin ecclesia, derived from the Greek ekklesia (ἐκκλησία), which means assembly1. Itself from the verb ekkaleô, "to summon, to call outside". Latin-speaking Christians have adopted the term as ecclesia2.

In the Septuagint, the Greek version of the Hebrew Bible dating from the 2nd century BC. AD, the Greek word ekklesia (church) designates an assembly called for religious reasons, often for worship. In this translation, the Greek ekklesia always corresponds to the Hebrew qahal which is however sometimes also translated as synagôgè (synagogue). For first-century Judaism, ekklesia immediately evokes the synagogue, to be understood as the assembly of God3. The words "church" and "synagogue" were thus two synonymous terms. They will only take on a different meaning because Christians will appropriate the word church, reserving that of synagogue for the assemblies of Jews who reject Christianity and from whom they are increasingly distinguished.

The word Church is written with a capital letter including in the plural when it designates one or more organizations, unlike the church, place of worship which designates from the third century the building where a community meets.