But despite the continuing debate on and offline, Oxford said the decision was cut and dried.
"Unfriend was chosen because it's much more common than defriend," Lauren Appelwick, a publicist with Oxford University Press, Inc., told ABCNews.com.
Though she couldn't elaborate on Oxford's methodology, she said the department responsible for tracking the use and evolution of language is very good at monitoring language trends.
"It's funny because there seem to be little clusters of people who have never heard the word "unfriend," she said, but added that research indicated that "unfriend is far, far more popular."
In announcing the word of the year, Oxford's Lindbery said, "Most "un-" prefixed words are adjectives (unacceptable, unpleasant), and there are certainly some familiar "un-" verbs (uncap, unpack), but "unfriend" is different from the norm. It assumes a verb sense of "friend" that is really not used (at least not since maybe the 17th century!)."
To some Facebook users (even those who prefer defriend), the dictionary's decision shows just how deeply social networks have infiltrated our lives.
"I think it's a cryptic example of how things like social networks are changing our relationships," said John Fischer, 27, a marketing strategist in New York City. "You used to have to deal with all the messy real-world parts of ending a friendship and now you can just click on a button and delete someone."