QStarDict, which stands for quasi-star dictionary, is a free (as in freedom) dictionary application. It is aimed primarily, but not exclusively, at those who learn foreign languages.
Features
Fuzzy search, cross-links, and history navigation
QStarDict not only finds words as soon as they are typed, but also shows fuzzy matches for them. It helps to identify similar words or correct typos. All articles are automatically cross-linked, so that click on a word in any article opens the corresponding article if it exists. With history navigation buttons it is easy to move back and forth between articles.
Add words to Anki
QStarDict has integration with Anki, which allows to create cards from dictionary articles.
Look up words from any application
If QStarDict is running under X server, it is possible to look up works from other applications using a popup window which is shown for selected words in any application.
Hide to notification area
To keep QStarDict always running with closed main window, it is possible to hide it to the notification area.
Extend with plugins
If you want to add new dictionary format or custom toolbar action to QStarDict, it can be done without modifying the core by writing a plugin.
Installation
QStarDict is available in Ubuntu, Debian and other distros repositories.
If you want to compile it yourself install Qt5 and GLib2 development files and run in the project's directory
qmake INSTALL_PREFIX=<your install prefix, /usr by default>
make
[sudo] make install
More information about installation: