The present research addresses a study one of the common linguistic phenomena in Coptic documents, which is represented in using linguistic synonyms between Coptic words and their Greek equivalents to express the same meaning. The research follows the linguistic analysis methodology for each synonym in terms of defining the meaning, classifying it grammatically and its linguistic derivation depending on the specialized Coptic and Greek dictionaries, then focus on these synonyms in published Coptic documents and then giving examples of them, and these synonyms will be divided into sets according to their types and uses, taking into account the alphabetical order in their study. The research aims primarily to conduct a comparative analytical study of these synonyms through the documents to determining the types of these synonyms and clarifying the subtle semantic differences between them. finding the reasons for the prevalence of this phenomenon, trying to find out some writing styles which common among the Copts, in addition to trying dating this phenomenon. Finally, the research hopes to be a nucleus for preparing a dictionary for the Coptic language that presents the material of its words according to the Coptic synonyms and their Greek equivalents.