Definition:
a seeming friend who is secretly an enemy
Examples:
"One whose hard heart is button'd up with steel; A fiend, a fury, pitiless and rough; A wolf, nay, worse, a fellow all in buff; A back-friend, a shoulder-clapper, one that countermands The passages of alleys, creeks and narrow lands." – William Shakespeare, A Comedy of Errors, 1623
About the Word:
The enemy posing as a friend has been a common enough creature that we have had a word for it for five hundred years or so. More recently, we’ve seen a rise in usage of the portmanteau frenemy ("one who pretends to be a friend but is actually an enemy.")
Although frenemy is of far more recent vintage than backfriend, it is not a creation of the 21st century. Frenemy can be found as far back as 1939, when an article in the August Chronicle stated "A frenemy is someone who's your friend today, but may be your enemy tomorrow."
