The Ubuntu Thesaurus Scope is an Unity Scope that allows users to easily search the Thesaurus for synonyms and antonyms or words. It uses the same API as the Dictionary app.
The best part is that Ubuntu Thesaurus Scope allows you to search words right from Unity home, without accessing a Lens first.
To install the Unity Thesaurus Scope plugin in your Ubuntu operating system, open a terminal window (hit the CTRL+ALT+T key combination) and paste the following commands (one by one, hitting Enter after each one):
sudo add-apt-repository ppa:scopes-packagers/ppa
sudo apt-get update && sudo apt-get -y install unity-scope-thesaurus
You will need to restart your session after the installation. This Lens is available only for the Ubuntu 12.04 LTS (Precise Pangolin) operating system.