from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. “in the work already quoted” — used, typically in footnotes and endnotes, to cite in an abbreviated form a source that has been cited previously; frequently abbreviated as op. cit.
From post-Classical Latin opere citātō ("in the work quoted"), ablative singular form of opus citātum ("quoted work”, “the work quoted"), from Classical Latin opus ("work") + citātum, neuter singular past participial form of citō ("I summon"); compare opus citatum, opere laudato, loco citato, locus citatus. (Wiktionary)