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The common good means the good of society

Circular illogic. Define it.

Personal good can be defined in the Aristotelian sense as that which makes a person happy.

[Nicomachean Ethics, Book 1, JT] For us it is clear that, from what has been said already, that happiness is one of those things that are precious and perfect. This view seems to be confirmed by the fact that it is a first principle, since everything else that any of us do, we do for its sake; and we hold that the first principle and cause of what is good is precious and divine.

This is the sense in which our Constitution refers to "Happiness." The common good then, would be that which maximizes happiness throughout society. The common good is more important than the personal good since the whole is greater and more perfect than its parts.

Aristotle said:

[Nicomachean Ethics, Book 8, TI, DR] All communities would seem to be parts of the political community. For people keep company for some advantage and to supply something contributing to their life. And it is for the sake of advantage that the political community too seems both to have come together originally and to endure, for this is what legislators aim at, and they call just that which is to the common advantage. All the communities, then, seem to be parts of the political community; and the particular kinds of friendship will correspond to the particular kinds of community.

The Catechism of the Catholic Church defines "Common Good" as " the sum total of social conditions which allow people, either as groups or as individuals, to reach their fulfillment more fully and more easily."

I would go even further. Aristotle lacked Christian revelation, and so his definition is slightly imprecise and incomplete. Personal "happiness" or fulfillment would be more accurately defined as conformity with God's will. The ultimate object of the personal desire for happiness then, is eternal life with God. Thus, the pursuit of the common good would be that which promotes the salvation of the souls organized in a society, although this definition does not necessarily require a State religion nor preclude religious freedom.

Aquinas said:

I answer that, As stated above (1), the law belongs to that which is a principle of human acts, because it is their rule and measure. Now as reason is a principle of human acts, so in reason itself there is something which is the principle in respect of all the rest: wherefore to this principle chiefly and mainly law must needs be referred. Now the first principle in practical matters, which are the object of the practical reason, is the last end: and the last end of human life is bliss or happiness, as stated above (2, 7; 3, 1). Consequently the law must needs regard principally the relationship to happiness. Moreover, since every part is ordained to the whole, as imperfect to perfect; and since one man is a part of the perfect community, the law must needs regard properly the relationship to universal happiness. Wherefore the Philosopher, in the above definition of legal matters mentions both happiness and the body politic: for he says (Ethic. v, 1) that we call those legal matters "just, which are adapted to produce and preserve happiness and its parts for the body politic": since the state is a perfect community, as he says in Polit. i, 1.
Now in every genus, that which belongs to it chiefly is the principle of the others, and the others belong to that genus in subordination to that thing: thus fire, which is chief among hot things, is the cause of heat in mixed bodies, and these are said to be hot in so far as they have a share of fire. Consequently, since the law is chiefly ordained to the common good, any other precept in regard to some individual work, must needs be devoid of the nature of a law, save in so far as it regards the common good. Therefore every law is ordained to the common good.