Like I said before; go to the meaning of the word (as understood by the signers of the Constitution)
From Meriam-Webster
a :a politically organized body of people usually occupying a definite territory; especially :one that is sovereign
Go to the Declaration of Independence
We, therefore, the Representatives of the united States of America, in General Congress, Assembled, appealing to the Supreme Judge of the world for the rectitude of our intentions, do, in the Name, and by Authority of the good People of these Colonies, solemnly publish and declare, That these united Colonies are, and of Right ought to be Free and Independent States, that they are Absolved from all Allegiance to the British Crown, and that all political connection between them and the State of Great Britain, is and ought to be totally dissolved; and that as Free and Independent States, they have full Power to levy War, conclude Peace, contract Alliances, establish Commerce, and to do all other Acts and Things which Independent States may of right do.
The signers of the Constitution had been through a war so that their colonies could become Sovereign States. They did not put a clause in the constitution saying they could leave the union because everyone understood that they were sovereign states and a sovereign state they had the power to negate a treaty. The Constitution is a treaty defining the compact between the states by which they will ”establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity,”
While we’re checking definitions let’s take a look at “Dual Sovereignty”: Dual sovereignty is a concept in the American constitutional framework that defines the relationships between the individual states and the federal government. It holds that both the State governments and the federal governments are sovereign with the states subordinate to the federal.
The state governments and the federal government each have spheres and can execute powers that the other cannot. The states are sovereign over most domestic issues—whether a will or contract is valid, what a landlord must do in order to evict a tennant, who is married, how old one must be to drive a car, and what the rules governing corporations are. The federal government is sovereign over issues such as trade between the states or foreign countries, foreign relations, etc.