One cannot access the Thesaurus on Libre Office 4.2.4 Its greyed out, have reinstalled, installed British dictionary, still greyed out. Help
It’s important to know what platform you’re on. See this AskLibO thread for Mac OSX (and a related one); for Ubuntu and related from AskUbuntu. There are further links in each of those threads. But if more help is needed, please do specify your OS.