Google Unofficial Dictionary API is now available to use on any website, side-project or whatever the motive is. It's an open source dictionary that uses the Google Unofficial Dictionary API and retrieve results over your website from Google's server.
Google Unofficial Dictionary API has an undocumented API that's used in Google Docs. As there is also developer built a Chrome extension that used Google Dictionary API to display the definitions, synonyms, nouns, verbs without opening a new page.
You can check out the live example of Google Unofficial Dictionary API, here. However, it looks like:
