Words are added to the wiki by users, there are thousands and thousands of things that need to be fixed or merged or have their alternatives added etc. manually and one by one by curators and you can help out by giving direct links on the forum or commenting on the discussion page for the word :)
@gabrielle5, actually should should now be able to just make those edits yourself anyway, regardless of whether you are a curator or not: anyone can make edits, and they are then sent to the "new changes patrol" to be checked by curators.
But I can certainly make you a curator as well! And I have done that, so you can now make changes and also you can patrol other people's suggested edits and accept of reject them.
@RabbitWho, sorry that you haven't seen the announcement - we need to make it much more prominent, clearly! Here is the announcement ont he "what's new" forum: http://www.memrise.com/thread/749556/
If you go to a wordset, or a word or a topic, you will now see a tab called "patrol". If you click it then you will be taken to the screen where you can review all of the changes that have been suggested in that topic; except that actually there is a bug in the Spanish patrol at the moment :( we will have that sorted out very very soon though.
Please let me know if you have any questions about it at all,