unfriend – verb – To remove someone as a ‘friend’ on a social networking site such as Facebook.

As in, “I decided to unfriend my roommate on Facebook after we had a fight.”

“It has both currency and potential longevity,” notes Christine
Lindberg, Senior Lexicographer for Oxford’s US dictionary program. “In
the online social networking context, its meaning is understood, so its
adoption as a modern verb form makes this an interesting choice for
Word of the Year. 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!). Unfriend has real lex-appeal.” —Oxford University Press blog