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Jesus replied to them, “Didn’t I choose you, the Twelve? Yet one of you is a devil.” He was referring to Judas, Simon Iscariot’s son, one of the Twelve, because he was going to betray him.
-John 6:70-71

Was Jesus saying that Judas was "devil-like"?  

The Greek word is transliterated 'diabolos'.

This same Greek word is used for slanderers:

Wives, likewise, should be worthy of respect, not slanderers, self-controlled, faithful in everything.
-1 Timothy 3:11

But know this: Hard times will come in the last days. For people will be lovers of self, lovers of money, boastful, proud, demeaning, disobedient to parents, ungrateful, unholy, unloving, irreconcilable, slanderers, without self-control, brutal, without love for what is good, traitors, reckless, conceited, lovers of pleasure rather than lovers of God, holding to the form of godliness but denying its power. Avoid 
these people.
-2 Timothy 3:1-5 (verse 3, slanderers)

'Devil-like' seems to mean being a slanderer: a person who slanders others, who falsely accuses them.  Jesus was saying that one of the disciples was a slanderer.

We know the story of Judas betrayal and how Satan entered into him, and it is easy to connect what Jesus is saying in John 6 to that.  But we have the same Greek word used in John 6 as in 1 and 2 Timothy.  No translation, at least on Bible Gateway, translates 1 Timothy 3, when Paul is talking about the wife of an elder, to say that these ladies should not be devils or devil-like or be a demon.  But is is the same Greek word 'diabolos'.  No translation has Paul writing in 2 Timothy, that in the last days, people will be 'devil like' or 'demons' or 'demonic'.

The apostasy of the last days will be characterized by a list of sins, Paul catalogs in 2 Timothy 3.  Among these is slanderers (diabolos).  Slander means false accusation.  Have you noticed the sin of false accusation, at this time?  And it has been a very popular sin since the beginning and is featured prominently in Judas betrayal of Jesus.  

Judas, even being very close to Jesus for those years, perhaps came under the influence of something false about Jesus.  Or did Judas always have a heart that lied about people for manipulative and destructive purposes?  Did he really believe something false and spread it or did he deliberately spread something false about Jesus?  The definition of slander seems to be that the person spreads, communicates lies about another person.  The destructive nature of slander that Judas seems to have employed is to tell others lies about Jesus and then they could either believe the lies or go along with them without fact checking so to speak.  And the lies would have fueled the conspiracy to 'get Jesus'.

Mark Twain had a saying that, "A lie can travel half way around the world before the truth puts on its shoes."  All sorts of destructive things are predicated on a lie.

I got this teaching by reading a book by Francis Frangipane: "It's time to End Church Splits", chapter 6; "One of You is a Gossip".