Are you having trouble reading and understanding your will without a lawyer standing next to you translating the latin and the legalese? Plain English has its advantages, but sometimes the unusual-sounding wills words have been used for so long and have been polished so nicely to mean exactly one thing that using them has its advantages too.
I noticed a blog post from http://www.allaboutestates.ca/ that defines a few of the more common latin phrases. And really "common" here means "frequently used" as there is nothing common about words in dead languages showing up in the things you're reading unless you're a lawyer. Click here to read the blog post, which I think you will find useful.