References for encyclopedias should include the following elements: author(s) or editor(s), date of publication, title of the entry, title of the work and pages, place of publication, and the name of the publisher.
For sources accessed online, include the retrieval date after the title as the entry may be edited over time, and add the URL.
In case the author is not available the entry of the title will take the place of the author.
Author, A. A., Author, B. B., & Author, C. C. (year). Title of entry. In Title of the Work (xx ed., Vol. xx, pp. x-xx). Place: Publisher.
McGhee, K., & McKay, G. (2007). Insects. In Encyclopedia of animals (pp. 170-171). Washington, DC: National Geographic Society.
Heuristic. (n.d.). In Merriam-Webster’s online dictionary (11th ed.). Retrieved from http://www.m-w.com/dictinoary/heuristic