Online Dictionary

Free cross-referenced definitions, spelling correction, and word searches from WordNet, Webster's, FOLDOC, and a variety of specialized sources.

Typing word.dict.die.net into your browser's location bar will show you a definition for word.
You can also use wildcards to find a word. ? will match any single character, while * will match zero or more. For example, if you know the word you are looking for starts with h, contains ist, and ends with c, you can ask for: h*ist*c
For quick dictionary lookups as you browse web pages, bookmark "Dictionary" either by right-clicking on the link and selecting "Add bookmark for link" or dragging it to your browser toolbar. You may then highlight any word on a page and select the Dictionary bookmark to see a definition.
If you have a lot of spare time, you may browse all entries by letter: # a b c d e f g h i j k l m n o p q r s t u v w x y z