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.

example:

[[synonyms:hello]]

i am attaching a screen capture to show what you get, when it is installed.

enjoy