If you refer to another person's writing or ideas when writing a paper, you must give that source credit by citing the work properly. This includes instances when you reference a dictionary. The many academic forms of citation include Modern Language Association, or MLA; American Psychological Association, or APA; the Chicago Manual of Style; and Harvard University style.
The Modern Language Association Handbook for Writers of Research Papers (7th edition), used typically in the humanities, requires that, when citing a dictionary entry, you initially state the word you defined in your paper. If the word has multiple definitions, include which one you used. Then provide the title, edition, publication year and medium of publication. (No page number is required, since the entry could easily be attained.)
For the works cited page, your entry should look like this:
“Apologize.” Def. 1. Merriam-Webster’s Collegiate Dictionary. 10th ed. 2000. Print.
Unless the dictionary has an author, it will be alphabetized in the list of works cited under the word or entry that you defined in your paper. Mention the word either in your text or in your parenthetical citation.
When citing a dictionary in APA format, which is most commonly used to cite sources in the social sciences, your entry on the bibliography page should use this format:
Word. (Copyright Year) Name of Dictionary (page number, edition). City Published: Publisher.
Demographic. (2008). Merriam-Webster’s Collegiate Dictionary (p. 223, 8th ed.). Springfield, MA: Encyclopedia Britannica.
To cite a dictionary within the text, use parenthetical citation. For example: (Name of author, year of publication). If there is no author, include the title: (Webster's, 1995).
An alternative method for in-text citation is to mention the name of your source within the text. For example: "According to Webster's dictionary (1995), …"
Chicago Manual of Style
Unlike many of the other academic formats that use parenthetical citations, Chicago style, which is often used in historical journals, uses footnotes and an endnotes page. Indicate footnotes with superscript numbers that appear after the punctuation to which the note refers. The entry should include the title in italics followed by a comma, the number of the edition followed by "ed." and a comma, the letters "s.v." and the title of the entry in quotation marks followed by a period inside the quotation marks.
For example: Webster's New International Dictionary, 3d ed., s.v. "revere."
In Harvard style, which is typically used in the sciences, when referencing a dictionary entry that does not have an author listed, provide the name of the dictionary in italics and the year it was published. Include these items in text; no entry is required in the reference list. For example:
The Webster Dictionary (1988) defines...
If the author of the entry is included, provide the author's last name and the publication year in parentheses. The reference list should provide the author, year of publication, title of the dictionary and publishing information.
In text: (Smith 2012) References: Smith, John. (2012) Oxford Dictionary, Vol. 4. 8th ed. Oxford: Oxford University Press, pp.758.