Wiktionary
Wiktionary is a multilingual, web-based project to create a free content dictionary, available in 158 languages.
This extension allows you to perform searches or look-ups without leaving the page.
this extension allows you to perform searches or lookups without leaving the page. simply hold alt (configurable) and double click a word, or select it. a small inline box will pop up with the results of your search or lookup.
this extension works for any search engine or online dictionary, and allows you to specify your own. as of now, the default selection contains only a few choices (wikipedia, answers.com, tfd.com, google, etc.) but feel free to suggest engines or dictionaries you find useful and i'll add them to the default list in future versions. of course, you don't have to wait, and can use your choice right away by specifying the url in the options page.
chrome-extension search-tool web-search online-dictionary