Format: 

Author, A. A. (Year of publication). Title of entry. In A. A. Editor & B. B. Editor (Eds.), Title of book (Pages). Retrieved from URL

Author, A. A. (Year of publication). Title of entry. In A. A. Editor & B. B. Editor (Eds.), Title of book (Pages). Location: Publisher.

Examples: 

Sustainability. (2012). In Oxford English Dictionary (3rd ed.). Retrieved from http://www.oed.com/view/Entry/299890

In-text: (Sustainability, 2012, Definition 2b)

The Walking Dead (tv series). (n.d.). In Wikipedia. Retrieved July 29, 2015, from https://en.wikipedia.org/w/index.php?title=The_Walking_Dead_(TV_series)

In-text: (The Walking Dead, 2015)

Jackson, M. (2002). Copyright. In J. R. Schement (Ed.), Encyclopedia of communication and information (Vol. 1, pp. 193-196). New York, NY: Macmillan Reference USA.

In-text: (Jackson, 2002, p. 194)

Notes: 

Provide only the year of publication unless the information may frequently change (e.g. Wikipedia); then, provide the full date of the last revision before the URL.

Source:
APA - 7.02 no. 27-30
APA (ER) - no. 21-25