A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Reference works
Parenthetical citations–reference list style: citing specific types of sources
Part II. Source Citation

Well-known reference works, such as major dictionaries and encyclopedias, should usually be cited only in parenthetical citations. You generally need not include them in your reference list, although you may choose to include a specific work that is critical to your argument or frequently cited. Omit the date, but specify the edition (if not the first). For an alphabetically arranged work such as an encyclopedia, cite the item (not the volume or page number) preceded by s.v. (sub verbo, “under the word”; pl. s.vv.)

P: (Encyclopaedia Britannica 15th ed., s.v. “Salvation”)

(Dictionary of American biography, s.v. “Wadsworth, Jeremiah”)

Treat reference works that are less well known as you would a book (see 19.1).

R: The Times guide to English style and usage. 1999. Rev. ed. London: Times Books.

Aulestia, Gorka. 1989. Basque English dictionary. Reno: University of Nevada Press.

P: (Times guide 1999, s.vv. “police ranks,” “postal addresses”)

(Aulestia 1989, 509)

Online versions of encyclopedias are regularly updated, so include both the URL and the date you accessed the material (see 15.4.1). Note that some reference works will indicate the appropriate URL to cite for a specific entry; use this rather than the less stable URL generated by search engines.

P: (Encyclopaedia Britannica online, s.v. “Sibelius, Jean,” http://www.britannica.com/ebc/article?tocId=9378608 [accessed June 1, 2005])