Word Tools: Thanks to the wonders of the internet, there are now various Latin word tools that will tell you not only what any Latin word means, but also that it happens to be a genitive singular future passive participle, or whatever the ‘case’ may be.
Whitaker’s Words – My personal favourite, partly because it does take into account some medieval spelling and vocabulary changes)
Health Advisory: While brilliant for making your way through a tricky translation, I would recommend using online word tools sparingly when it comes to actual Latin study – it’s easy to get dependent and forget to actually learn the vocabulary and grammar yourself, which comes back to haunt you later . . .
Dictionaries: Most Latin-English dictionaries only reflect classical usage and vocabulary. The best dictionary for medieval Latin is the recently completed Dictionary of Medieval Latin from British Sources (DMLBS) published by Oxford University Press, which is also available as a subscription service online and through the Latin/Greek online dictionary search Logeion.