[Shifted to haskell-cafe.] G'day all. Quoting "Benjamin L.Russell" :

According to the Merriam-Webster Online Dictionary, it is "topoi" (see http://www.merriam-webster.com/dictionary/topos).

Topoi form a certain class of category. You can study topous, you can prove theorems about topois and you can discover properties of topon. (That last one is an omega, so it's pronounced more like "top-own".)

Where did you find "octoposi?"

In my ancient copy of Liddell and Scott. Here's the online entry: http://tinyurl.com/ck8gst Cheers, Andrew Bromage