We are all tempted to use encyclopedias, dictionaries...... and yes, quelle horreur!!! ...even wikipedia when writing essays or posting to a discussion group.
So I thought I would say a few words on these resources. Unlike many instructors I do not entirely disparage wikipedia... but the caution I will post here applies to it as well as more usual encyclopedias and dictionaries.
All three of the resources are useful ONLY to give a you quick background into a topic which is unfamiliar... but none of them should be used to prove a point in an essay or in a discussion. The reason for this has nothing to do with how rigorously the facts in each type of source are checked and double-checked. The basic problem with them as source is they are syntheses of the work of many scholars... and often will give you only one version on a debatable topic - and you may not be able to trace which part of each article was written by which scholar. Wikipedia has additional problems in that it is rarely double and triple checked and is only rarely produced by scholars who are trained to think carefully and speak only when they have checked as many sources as possible. Wikipedia does have the strength that often it lists scholarly sources at the bottom of the article....
So use wikipedia! Use standard encyclopedias! Use dictionaries!
BUT only to give yourself a quick overview of a topic - then go to scholarly sources for your essay or discussion posting.