This father, about A. D. 170, wrote a letter to the Roman church, in which are found these words:- TFTC 52.1
“We passed this holy Lord’s day, in which we read your letter, from the constant reading of which we shall be able to draw admonition, even as from the reading of the former one you sent us written through Clement.” TFTC 52.2
This is the earliest use of the term Lord’s day to be found in the fathers. But it cannot be called a decisive testimony that Sunday was thus called at this date, inasmuch as every writer who precedes Dionysius calls it “first day of the week,” “eighth day,” or “Sunday,” but never once by this title; and Dionysius says nothing to indicate that Sunday was intended, or to show that he did not refer to that day which alone has the right to be called “the Lord’s holy day.” Isaiah 58:13. We have found several express testimonies to the sacredness of the Sabbath in the writers already examined. TFTC 52.3