Mike Ash is shipping a new app for Mac users, LiveDictionary 1.0. LiveDictionary is a Sarafi extension utility designed for Web based definition searching. The app features background transparency and support for various dictionary types. According to Mike Ash:
LiveDictionary 1.0 released.
LiveDictionary is a Safari extension that adds fast, convenient dictionary lookups to the Web. Once installed, it becomes a transparent part of Safari; point to a word with the mouse cursor, and its definition or translation appears in a popup window. LiveDictionary offers a wide array of dictionaries for technical terms, general language, and bilingual usage.
You can find more information about the LiveDictionary release at the Mike Ash Web site. LiveDictionary 1.0 is available for US$25.00.