this filter can be used by teachers to select words in the text
which will get a dashed underline (visual mark) and when a user
hovers over the word he/she will get a tooltip (html title tag)
of the synonyms for that word.
using the ( semi free ) API and services of http://words.bighugelabs.com
here you can apply for an up to 10000 queries a day free API key
and put it into the filter's code for it to work properly.
to use it:
add [[synonyms: before the word and ]] after the word.
i am attaching a screen capture to show what you get, when it is installed.