I just tried this. In the Dictionary application where the word is typeset like this "dic.tion.ar.y" it is possible to right click only on a section of the word but it is still possible to bring up the "Start Speaking" contextual menu item and it will speak the whole word. In the thesaurus section the whole word can be highlighted and read aloud in the usual way.
This is all on OS X 10.5.8. Are you using another version?