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1814, from Italian, literally "sweet doing nothing." The Latin roots are dulcis "sweet" (see dulcet), facere "to make, do," and nec entem, literally "not a being."
This phrase, frequent enough in English literature, does not seem to occur in any Italian author of note. Howells says that he found it current among Neapolitan lazzaroni, but it is not included in any collection of Italian proverbial sayings. [Walsh]