I was looking for a good portable dictionary for my iPhone, and I’ve found a couple of programs. One is great, one is free. If you’re going to use either one of these, make sure you install the Japanese keyboard and the Chinese Traditional “draw the kanji” keyboard on your iPhone, and take the time to learn how to use them.
For starters, there’s Kotoba!, which is a very basic free dictionary that is “based off of Jim Breen’s JMDict.” JMDict is essentially EDICT, which isn’t a professionally edited dictionary. But it is free, and it is Japanese->English. The definitions are very stripped-down, and sometimes confusing or misleading, and sometimes just wrong.
But did I mention that it’s free?
Daijirin is Awesome
If you’re beyond the beginner phase of learning Japanese, and if you’re comfortable using Japanese->Japanese dictionaries, I highly recommend the 大辞林 (Daijirin) dictionary, which is available from the iTunes app store as well for $12.99 US. It takes a little getting used to at first, but once you get comfortable with the interface, you’ll realize just how great it is.
For example: even if your Japanese isn’t as strong as you’d like, you can touch-select words in the definition you don’t understand, and it will allow you to jump to the definition. You can keep jumping until you figure everything out, then jump back to the original definition.
This is a great way to pick up a lot of new vocabulary, and gets you more proficient at using Japanese->Japanese dictionaries, which are always better at explaining Japanese words than Japanese->English dictionaries.
The best part about the 大辞林 is that you don’t have to shell out $300 for a portable electronic dictionary to get it, which is how it usually comes, and it means one less thing to carry around.