Although Gnome comes with a dictionary application, it's not the most polished tool out there. Its major shortcoming is the lack of text formatting, which makes dictionary articles more difficult to read. Enter the Purple dictionary application. Developed as a part of the Elementary project, this lightweight and slick dictionary tool is perfect for quickly looking up words from the convenience of your desktop.

While Purple is decidedly a bare-bones application, it presents articles as nicely formatted text. In addition to that, the left sidebar provides quick access to previous articles and the Bookmark feature lets you bookmark articles for later use. Purple's binary packages for Ubuntu are available through a PPA, so installing the application on Ubuntu Linux and its derivatives is a matter of two commands:

sudo add-apt-repository ppa:aroman/purple 
sudo apt-get update && sudo apt-get install purple

Purple is not perfect, though. For example, each article provides a list of synonyms (where available), but they are not hyperlinked. You can't switch between different dictionary sources either. But if you are willing to look past these shortcomings, you might find Purple a handy tool.

Via OMG! Ubuntu!