urban dictionary

Merriam-Webster Dictionary Widget looks up words in English.

Japanese dictionary and kanji lookup tool.

Comprehensive thesaurus and dictionary.

Dynamic rhyming dictionary.

Bookmark words in Dictionary.app.

Spelling, grammar, dictionary, and more.

Your multilingual dictionary essential for your Mac.

Keep Your Word lets you build your own dictionary.

Simple interface to A Latin Dictionary, by Lewis and Short.

JEDict 4 is multilingual dictionary capable to search any plain text files.