DOMINICUM. - The oldest places where Christians held their gatherings and celebrated the divine mysteries were private domus, which were variously called: οἶκος, domus Ecclesiae, domus Dei, domus orationis.
D. (κυριακόν = “that which belongs to the Lord”) perhaps implies the word conventiculum or another similar term. Like the word ἐκκλησία, it means an assembly and, subsequently, 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 everything that was the property of, or pertained to, the Emperor. S. Cipriano, in the treatise De opere et eleemosyma (Opera, I, Vienna 1868, p. 384), writes: « In dominico 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 Constantini imperatoris basilica facta est, id est d., mirae pulchritudinis » (to explain the word basilica, recourse is made to the more familiar synonym). Still in the Chronicon of s. Girolamo (PL 27, 678 and 682), one reads: « in Antiochia d., quod vocatur aureum, aedificari coeptum ».
The sole example in the field of epigraphy to be noted with regard to the term is a Roman inscription engraved on a slave’s collar, attributed by De Rossi to the first half of the 4th century.