Download from PortableApps.com
Artha Portable can run from a cloud folder, external drive, or local folder without installing into Windows. It's even better with the PortableApps.com Platform for easy installs and automatic updates.
Artha is a handly offline thesaurus with support for regular expression lookups. It runs from the system tray in the background and can be accessed using a hotkey after highlighting a word in any app.