You could argue that there's not much need for a separate dictionary app any more. With dictionary services built into nearly every interface and Google and Wikipedia searches just a tap away, it's not hard to find out what a word means or how it's spelled any more. But sometimes you may just want to browse around or look a word up for yourself, and for those times, there's the Merriam-Webster Dictionary app, which is now available on the iPad for free.
It's certainly not the only dictionary app available, and the renowned Oxford English Dictionary has its ow