The word comes from two words -- "anti" and "nomos", which means "law. You can find antinomianism in churches all around us. Andy Stanley implies it, when he says we should disengage from the Old Testament. Former pastor of Coral Ridge Presbyterian church Tullian Tchividijian preached it. The so-called "hyper-grace" movement in Charismatic circles proclaims a form of it.
And you can find a form of it, generations ago, in the writing of Dallas Theological Seminary founder Dr. Lewis Sperry Chafer. Consider the following ideas taught in Dr. Chafer's book, Grace, The Glorious Theme (first published in 1922).
Chafer wrote that Christ's death absolutely dealt all the sins of all people, so as a result God is freed to show grace to all. He also said the cross "absolutely" (his word) removed the condemnation of all sin from all people.
Chafer's teaching helps me understand why some Christians I've met in the past insisted that the sole cause of condemnation is conscious unbelief toward Christ, and nothing else. I can see why they said that. If Christ has already taken away all condemnation from all people, so what else is left that could condemn you but conscious rejection of Christ?
But Romans 2 says God will judge Gentiles against the standard of the moral law they carry in their hearts, and Jews by the same, and by Scripture. Revelation 20 says God will judge the lost according to their works ("works" in the plural, not just unbelief).
God justifies the individual (not en masse) of all his or hersins (not just one) only when he or she trusts in Christ. Christ's death is the historical basis of God's forgiveness. It makes justification possible. But your condemnation is removed only when you are in Christ (Romans 8:1). Until then, you were just as condemned as anyone else (Ephesians 2:1-3, "even as the rest").
Dr. Chafer goes on in his chapter to say something true -- that saving grace is a pure gift, received by faith only, with no law-keeping obligations attached to it. This is true. You do not need to keep any of the 10 Commandments in addition to trusting Christ, in order to become saved or keep-on being saved.
However, it is possible to distort this core Gospel grace. Many of Dr. Chafer's doctrinal descendant say, through pulpit and pen, that the faith that obtains justification of sin isn't related to moral behavior at all. Any causal connection between faith and good works is broken.
These preachers, who stand in Chafer's legacy, build an iron wall between justification of sin and practical holiness of heart. Not everyone in Chafer's tradition teaches this, but a lot of them do. (Many of this group call it the "Free Grace" movement). This idea is heretical, contradicts James 2, and needs to be stamped out.
Yes, justification isn't the same thing as heart-holiness; that is Catholicism.
But justification is never severed from heart-holiness, either. Faith in Christ obtains God's justification, which always results in the Holy Spirit immediately making us new creations in Christ. Always.
Justification and sanctification are distinct works of God. They shouldn't be blurred together, because that is legalism. But they aren't totally disengaged from each other, either. That is antinomianism.
This is why John, in 1st John 3, said that godly living is an index of whether someone is a true child of God (the other index being a credible profession of faith in Jesus Christ and the Gospel). Faith alone justifies, but justifying faith always lives itself out through obedience to God.
(Dr. Chafer also confuses by treating all grace in Scripture as unconditional. That word "unconditional" needs careful definition. Sometimes God shows grace in a completely unconditional way. God chose Jacob as covenant-head based on nothing but His own will (Romans 9:11). But in other scriptures God says He opposes the proud but gives grace to the humble (James 4:6). Paul said God showed him mercy because he was ignorant, 1 Timothy 1:13. So something in Paul's psychology played a role in whether God showed him mercy. But this subject deserves distinct attention).