DebianGnu comes with gcide, dictd, dict and jargon. I think that these packages should be installed by default - or at least mentioned at the installation, and strongly recommended -, but instead they come in Woody's 4th CD and many users never hear about them.
About something more urgent: I'm teaching in a university at the outskirts of Rio de Janeiro where only a few students can read English. I'm thinking about doing a few tweaks on dictionary.el and using it there, with both gcide and freedict.
Tuesday, 2004may18: another idea: the students will be using Emacs on
W$ boxes, and I'm not famililiar enough with W$ to risk installing
dictionary servers and clients there - chances are that I would
spending dozens of hours working on that and not complete the task. A
simple alternative is to make the dictionary from
../e/dict.e.html#english-to-portuguese available as a text file and teach the
students to find stuff there with C-s