Ninjawords is an online dictionary, open the site and simply key in your word to get the meaning. The definitions come from the fast-growing Wiktionary. If Wiktionary does not have the definition, they use Princeton WordNet dictionary.
The beauty of Ninjawords is:

• It is quite fast and hardly takes any time to display the meaning of word.
• You can find the meaning of multiple words with a single click, you just need to type multiple words separated by commas in the search field, and hit the look up button, to see the meanings of all the words.

• You can simply use this service to learn new word as well, by clicking “random” button adjacent to “look up” button.

• You can also search the words by directly typing them in url in the format given below. “http://ninjawords.com/word1, word2, word3” Here word1, word2, word3 refer to the words which you want to look up.

This is all about Ninjawords, I found it very Fast, Convenient and appropriate as well.What do you think about this service, have your say.