DOMINICUM. - The earliest places where Christians held their gatherings and celebrated the divine mysteries were private houses, which were variously called: oikos, domus Ecclesiae, domus Dei, domus orationis.
D. (χυραχάω = “belonging to the Lord”) perhaps implies the word conventiculum or something similar. Like the word ἐκκλησία, it means a gathering and, later, the place of assembly. The concept it expresses is the same as that of domus Dei. This meaning ceased at the end of the 4th century, when the name was used to indicate anything that was the property of the Emperor and pertained to him. St. Cyprian, in the treatise De opere et eleemosyna (Opera, I, Vienna 1868, p. 384), writes: “In dominio sine sacrificio venis.” The Itinerarium Hierosolymitanum (CSEL, XXXIX, p. 23), written around 333, concerning the Constantinian basilica of the Holy Sepulchre, states: “Ibi modo iussu Constantinii imperatoris basilica facta est, id est d., mirae pulchritudinis” (to explain the word basilica, recourse is had to the more familiar synonym). In the Chronicon of St. Jerome (PL 27, 678 and 682) one reads: “in Antiochia d., quod vocatur aureum, aedificari coeptum.”
The only example in the field of epigraphy to be noted regarding the word is a Roman inscription engraved on a slave’s collar, attributed by De Rossi to the first half of the 4th century.