The dictionary of obscure sorrows
Hexadecimal colours and their corresponding dictionary definitions. Cute.
This could be a handy: a client-side spellchecker. The dictionary files are a bit big of course—maybe local storage could help.
It's The Meaning Of Liff all over again. Creating and rating neologisms.
British English slang dictionary with translations into American English.
Put all those years of reading science fiction to use. Help track down first usage of sci-fi terms.
The word w00t has been voted Merriam-Webster word of the year 2007. Slow year.
Happy Cog redesigns Dictionary.com and its siblings.