Japanese/Kanji Dictionary
This library provides a simple interface to a subset of the information stored in Jim Breen's JMDICT and KANJIDIC2 dictionary files. For better loading time, it can also read and write dictionary files in its own format, which is essentially just a stripped down version of the normal format.
There's also a Windows Forms Kanji control. It looks like this:
Japanese/Kanji Dictionary's license is Zlib-style. JMDICT and KANJIDIC2 have different licensing; see here for more information.