https://www.ligonier.org/learn/devotionals/our-ethical-basis/ "Dr. R.C. Sproul notes that Christian ethics are theonomic, that is, governed by God’s law. This does not mean the church is called to institute a theocracy in the civil realm. It does mean that no correct ethical decision can be made apart from reflection on God’s law. Many Christians neglect the study of the law of the Lord, but if we do not seek to understand His commandments, we will lack the wisdom needed to discern between right and wrong in our decisions."
Or as explained in more detail below;
https://www.ligonier.org/learn/devotionals/basics-ethics/
"According to Scripture, ethics are theonomic — determined not by the self but by the Lord. God’s standard alone provides the absolutes for our conduct.
This standard exists outside of us and is binding upon all, regardless of whether or not one believes Scripture.
All men, because they are in Adam (Rom. 5:12), are bound by the covenant of works and will be judged according to their obedience. We may choose to disregard this relationship’s obligations, but we cannot destroy them.
Scripture reveals to us a transcendent law that remains binding upon all and is based on our Creator’s holy character. These stipulations do not exist outside of Himself; they are part of His eternal nature. This law, often known as the moral law in the Reformed tradition, is the “law of Christ” (Gal. 6:2) and can be found in the Ten Commandments and in the ethical imperatives of the apostles.
Finally, when we say all Christians are theonomic, we are not endorsing theonomy, a movement that says the old covenant’s civil penalties remain in force. Believers may legitimately debate this issue, but all must be “theonomists” in the sense of affirming the permanent validity of God’s moral standards (1 Cor. 6:9–10).“
Thus I would be a lower case "theonomist,” in the sense of affirming the permanent validity of God’s moral standards (1 Cor. 6:9–10). However, I am not a "theonomist," in the sense used by The so-called "Theonomy movement." The latter use of the term was inappropriately and inaccurately taken to mean Reconstruction or taking Dominion by misapropriating Van Til.
https://feedingonchrist.org/theonomy-two-kingdom-and-a-middle-road/ "In contrast to the “spirituality doctrine” and “Two Kingdoms theology,” there is the Christian Reconstructionist movement of the 1970’s. This twisting and contortion of what theonomy means was an attempt, albeit inaccurate, to apply Van Tillianism to the political sphere. Cornelius Van Til, the great Reformed apologist from Westminster Theological Seminary in Philadelphia, boldly asserted that there was no such thing as “natural law,” rather there is only God’s law. He even went so far as to say “you are either autonomous or theonomist.” He did not mean what the movement says he meant. Van Til was simply asserting that God’s word is authoritative for every sphere of life. What the Reconstructionists miss in Van Til’s theology is the role of common grace in regard to the moral law and politics. Van Til constantly pointed out the fact that the law of God, the Ten Commandments, were written on the heart of all men by nature. While men hate the fact that they are the Imago Dei, they can never escape the implications of the fact that they descended from Adam and had a conscience that bore witness to the law of God (Romans 2:15). How could ungodly governements enacted righteous laws throughout the centuries? This is where Van Til’s empahsis on common grace comes in. Paul could say of Nero that he was God’s minister to punish evil and reward good–not because he was reading the Bible and implementing the Old Covenant civil law, but because he was made int he image of God and by common grace acknowledged to some extent right and wrong in God’s world."
"The Theonomy movement" is a horrendous redefining of the original meanings of those whom coined the terms theonomic, theonomist, theonomism and even theonomy. It is also even a distorting of the term Theocracy which literally means ruled by God. The only true Theocracy exists when Christ returns to physically reign and rule with the Culmination of all things at the end of all things.
What they really believe in is called Reconstructionism or Domionism/Kingdom Now Theology.
https://www.gotquestions.org/dominion-theology.html
https://www.gotquestions.org/kingdom-now.html
https://www.desiringgod.org/articles/dominion-theology-or-reconstructionism
Proponents of the "Theonomy Movement" appropriated the terms theonomic and theonomist from people that fell under the Natural Law tradition.
This could have been a simple misunderstanding of Van Til's applications by Brothers and Sisters in the Faith. The term theonomy historically simply means God’s Law and Morals. Theo meaning God and nomy meaning Law.
Theonomy, prior to the Christian Reconstructionists was defined the same way theonomic and theonomist was used by Ligioner Ministries or Cornelius Van Til. Which is not compatible with the redefinition within Reconstructionist or Domionism theology.
I am theonomic, a theonomist in that sense and in that form agree with the idea of theonomy when it means simply living by God's Law and Holy Word. However, if you mean the Reconstruction co-opted "Theonomy movement," I would not go near it with a million foot pole.