You could add the glosary module to the list of possibilities. In brief,
Forum: everibody could post. Anibody could edit THEIR posts but only during the next 30'. Nobody could edit the post of others (they could add new post as reply).
Glosary: everibody could post. Anibody could edit THEIR posts allways. Nobody could edit the post of others (they could add commnets or new entries)
Wiki: everybody and everytime could post and edit what they or others write.
Wiki
Is wiki the best way to approach this problem?
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