Encyclopedias and dictionaries can be difficult to cite because there are a number of points to consider. Is the reference item: in print, online, or both (i.e., in print and online), edited, and does the entry in an encyclopedia have an author?
The following are patterns for how you might write a reference list entry for articles from a encyclopedia or an item from a dictionary.
Title of entry. (Year Published). In Title of reference work (xx ed., Vol. xx, pp. xxx-xxx.). Location: Publisher.
Title of entry. (Year Published). In Title of reference work (xx ed., Vol. xx, pp. xxx-xxx.). Retrieved from http://www.xxxxxxxxx
Progressive education. (2013). In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/topic/478341/progressive-education
(American Psychological Association, 2010, pp. 79, 204-205)