Cite the dictionary on your Works Cited page by including the entry in quotation marks, the publisher and date of publication, the word "Web" and the date of access. For example, "atrabilious." Oxford Dictionaries Online. Oxford University Press, 2011. Web. 17 June 2011.
Include a URL in angle brackets only if your professor requests it. For example, "atrabilious." Oxford Dictionaries Online. Oxford University Press, 2011. Web. 17 June 2011 <http://oxforddictionaries.com/definition/atrabilious?region=us>.
Cite the dictionary in your text by placing the word in quotation marks and parentheses at the point of reference. For example, Bile being the referent in question ("atrabilious").