I saw the movie of The Da Vinci Code the other day, which led eventually to my reading the Wikipedia entry on the (fictional, as it turns out) organization known as the Priory of Sion. The article describes the organization as (among other things) "a modern Rosicrucian-esque ludibrium." The term clearly had something to do with games (derived from Latin "ludus," related to play, as in Hesse's Magister Ludi, and also a root of words like "ludicrous"), but I wasn't sure what, so I followed the link to the ludibrium article. (The term is not in MW3 (unabridged) nor in MW11. Interesting.)
The Wikipedia article defines "ludibrium" as "a plaything or a trivial game," but then goes on to apply the term to the third Rosicrucian Manifesto, to the Situationist International, and to the Priory of Sion, so I'm guessing it can also refer to elaborate hoaxes that in some sense are treated like, or feel like, games. Apparently Frances Yates (author of Giordano Bruno and the Hermetic Tradition and The Art of Memory, both of which I really ought to read someday) indicated that (to quote Wikipedia) "the term implies more some sort of Divine Comedy, a dramatic allegory played in the political domain." I have no clear idea what that means, or what it has to do with playthings or games. I'm really falling down on the job here, aren't I? I'll try to do better.