The authors agree that this surname originates in the term that designates the monk or religious. F. Miranda specifies that its fixing as a surname is earlier than the 14th century and derives probably from the nickname of a first bearer linked to the fact of living near a monastery or of working in premises belonging to monks. He notes that the term goes back to the Late Latin ecclesiastical monachus, taken from the Greek monakhós (μοναχός), itself derived from mónos (μόνος), "single, solitary". G. Rohlfs also points to the Greek μοναχός ("monk") as etymon and notes that the surname has a Greco-Byzantine character, with a presence documented in Lucania, in the locality of Avigliano.

E. De Felice broadens the perspective by indicating that the surname could have been formed from names of religious condition and rank, from nicknames, or else from the various extended or figurative senses that the term presented according to the region. He mentions the variant Monego (with the feminine form mónega), proper to Veneto. For his part, R. Brondolo records for northern Italy the dialect word monich, in the sense of "sacristan" or "person in charge of the church", as the base of the surname in that area.

Miranda further highlights a series of regional meanings of the common term monaco in Sicily: at Syracuse it designated the frame used to hold the bed-warmer; at Catania, a small oil lamp left burning during the night; at Agrigento, a wooden clamp for closing doors and windows; and at Enna, the main beam of the pitched roof. These figurative or extended uses of the term may have given rise to nicknames and, subsequently, to surnames in different areas of the island.

As for its geographical distribution, Miranda describes it as a surname of pan-Italian presence, although with a greater concentration in the centre and south of the peninsula. It appears in Campania, Sicily, Puglia, Lazio, Lombardy, Abruzzo, Piedmont, Calabria, Tuscany, Emilia-Romagna, Basilicata and Veneto. In Sicily it is documented in all the provinces, with a greater density in those of Catania, Syracuse, Trapani, Messina and Palermo. De Felice confirms the high frequency in the south, where the forms with the article Lo Monaco and La Monaco, characteristic of that area, are also recorded.