English Dictionary Lookup


This extension allows for easy lookup and display of English word definitions within webpages via an unobtrusive dialog box. All the dictionary data (over 13MB compressed) is located within the add-on, so this add-on will never connect to an external site and can operate without an internet connection.

To use this add-on, simply double-click on any word within a webpage and, if it is found in the dictionary, a dialog box will show up in the middle of the screen containing the word definition. Click anywhere outside the dialog box to dismiss the dialog. You can also lookup words inside of the dialog box by double-clicking on them. Please note that the word must be selectable for the add-on to recognize it.

The definition dialog box contains a header with page links that allow you to quickly jump to word synonyms or other word forms if they are available. These links are named as abbreviated parts of speech (i.e. n. for noun, v. for verb, and for “participle present & verbal noun”). Simply click on the links to jump to the relevant sections within the dialog. The header also includes a bracketed word with left arrow; this is the word that was defined previously and works as a back button if this word is double-clicked.

This add-on would not be possible without the GNU Collaborative International Dictionary of English (GCIDE) ( and by extension the GCIDE_XML (

Please note that the source dictionary data is sometimes incomplete. Missing symbols or characters will show up as unicode question marks. Also note that this add-on uses an algorithm to find word roots if the searched word is inflected. This algorithm is not perfect and will sometimes fail to find a root word or find the wrong root word. Lookup accuracy may improve through future updates.

Thank you for your interest in this add-on and I hope you will find it of good use.

English Dictionary Lookup
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