OneAcross Puzzle Dictionary

OneAcross.com is a great website for crossword puzzle afficanados.

Wiktionary

Wiktionary contains over a million entries with English definitions from over 295 languages. It also includes a thesaurus, a rhyme guide, phrase books, etymologies, abbreviations and more.

Pseudodictionary

A fun site for made up words, pseudodictionary allows the submission of words for inclusion.

Artcyclopedia

Search or browse this art resource by artist's name, title of work, museum, historical period or movement. Artist must have work in a museum to be included.

OneLookDictionary

OneLook contains and index of 900 online dictionaries with over 5 million words.

TheFreeDictionary.com

Hosted by Farlex, TheFreeDictionary.com is very comprehensive and allows searching of general and subject dictionaries, including foreign language, thesauri and encyclopedias. Includes idioms and acronyms.