The Publication Manual of the American Psychological Association, or APA, outlines the APA's general format for research papers, in-text citations, notes and reference pages. This format is known as APA style and is most commonly used in the social sciences. Citing an online dictionary differs from citing a physical dictionary in that no publishing information is required---only the defined word, the name of the dictionary and the URL.
Cite the online dictionary in the "Reference List" in the following format: Title of entry. (Year of publication). In Title of dictionary. Retrieved Month Day, Year, from URL. For example, "Materialism. (2010). In Merriam-Webster's Collegiate Dictionary. Retrieved July 26, 2010, from http://www.britannica.com/dictionary?book=Dictionary" with no final period. The name of the dictionary should be in italics.
Place the citation in the "Reference List" in alphabetical order according to the first letter of the definition.
Cite the definition in the text by placing the defined word and the date of publication in parentheses after the relevant phrase, before the punctuation mark.
The date of publication is often not listed. If this is the case, use the abbreviation "n.d." (which stands for "no date").
The date listed in the actual definition is not the date of publication, but the date of earliest use. Do not use this in your citation.