2002 September 19, "grampus", “"OT: What is a #!%$*& "cookie"?"”, in rec.radio.shortwave[1] (Usenet), retrieved 2008-03-21:
And unlike Jonah, dozens of my incisive life-affirming cancer-curing magnum opi are still entombed in the bowels of this pitiless machine and millions of respondents don't even know how disappointed they are not to read them.
2003 July 15–21, Mary Burns, “Falling Water, Crashing Windows: Making Computers More School Friendly”, in ACM Ubiquity[2], volume 4, number 21, →ISSN:
First, we educators need to reject the canon that computers are magnum opi whose limitations should be rationalized and overlooked.
2006 December 7, "Agent Smith", “Re: Hidden Code in The Bells”, in rec.org.mensa[3] (Usenet), retrieved 2008-03-21:
If the number of humans is infinite, you've got Shakespeare, politely cranking out his magnum opi. QED.
2008 January 17, "tcbevol...@yahoo.com", “The National Police Gazette”, in alt.fan.rawilson[4] (Usenet), retrieved 2008-03-21:
As we all know, Joyce's magnum opi Ulysse and Finnegans Wake are commonly thought difficult and obscure.
Usage notes
Magnum opi
is an erroneous Latin form, taking the noun as second declension instead of third, and ignoring the adjective inflection. The correct Latin plural, also used in English, would be magna opera.