vim-online-thesaurus

The plugin provides the :OnlineThesaurusCurrentWord command to look up the current word under the cursor in an online thesaurus. Alternatively, you can look up any word with :Thesaurus word.

Internally, both commands make a request to http://thesaurus.com/, parse the results, and display them in a vertical split in the bottom.

By default the :OnlineThesaurusCurrentWord command is mapped to <LocalLeader>K. If you haven't remapped <LocalLeader>, it defaults to \. To close the split, just press q.