Definition of "unfriend"

unfriend¹

/ˈʌnfɹɛnd/

noun
plural unfriends
1. One who is not a friend; an enemy.
  Quotations
  It is even as I suspected, my lord, […] Ye have back-friends, my lord, that is, unfriends—or, to be plain, enemies—about the person of the Prince.
  1822 May 29, [Walter Scott], chapter IV, in The Fortunes of Nigel. […], volume II, Edinburgh: […] [James Ballantyne and Co.] for Archibald Constable and Co.; London: Hurst, Robinson, and Co., pages 88–89
  I wonder often it has not drawn her out of the grave to come and stand before me, and hear me tell her how I loved her. For, sir, we parted unfriends.
  1856, Elizabeth Gaskell, The Poor Clare
  Thus many unfriends and some friends of the Capital agree upon the same policy with diverse and contradictory motives […]
  1916, William Edwin Chilton, John Downey Works, Fiscal relation between the United States and the District of Columbia
  The unfriend betrays me, ignores me, denies me, breaks me down; the unfriend is against and tries to devour my personhood.
  1999, Kees Waaijman, John Vriend, The mystical space of Carmel

unfriend²

/ʌnˈfɹɛnd/

verb
third-person singular simple present unfriends, present participle unfriending, simple past and past participle unfriended
1. (rare) To sever as friends.
  Quotations
  "I hope, sir, that we are not mutually Unfriended by this Difference which hath happened betwixt us."
  1659, Thomas Fuller, The Appeal of Injured Innocence
2. (social media) To defriend; to remove from one's friends list (e.g. on a social networking website).
  Quotations
  "I asked her why, she said it was because I didn't comment, and I shrugged and said whatever. I didn't unfriend her."
  2007, Mia Consalvo, Caroline Haythornthwaite, Internet Research Annual: Volume 4
  Without unfriending someone, you can now choose to limit or block (unsubscribe) someone from your newsfeed or choose to see only what Facebook deems as very important.
  2013, Nils Smith, Social Media Guide for Ministry: What It Is and How to Use It