Look up a word in an online dictionary. Write down the online resource, its edition, volume and the number of the definition you are using if there are multiple examples.
Write the word you looked up in quotation marks, with a period after the word but within the quotes. For example: "Doctor."
Add the name of your online dictionary source, underline it and add a period to the end of that portion of the citation. For example, if you used the Webster's Dictionary you would write the citation as: "Doctor." Webster's Dictionary.
If there was a specific definition used then that would be written as: "Doctor." Def. 1. Webster's Dictionary.
Note: Webster's Dictionary would be underlined in both cases.
Add to the citation the name of the edition and year of publication. To write the citation in it's entirety, it would look like this: "Doctor." Def. 1. Webster's Dictionary. 2nd ed. 2008
Note: Webster's Dictionary would be underlined.