Objection 1. It seems that these names applied to God are synonymous names. For synonymous names are those which mean exactly the same. But these names applied to God mean entirely the same thing in God; for the goodness of God is His essence, and likewise it is His wisdom. Therefore these names are entirely synonymous.
Objection 2. Further, if it be said these names signify one and the same thing in reality, but differ in idea, it can be objected that an idea to which no reality corresponds is a vain notion. Therefore if these ideas are many, and the thing is one, it seems also that all these ideas are vain notions.
Objection 3. Further, a thing which is one in reality and in idea, is more one than what is one in reality and many in idea. But God is supremely one. Therefore it seems that He is not one in reality and many in idea; and thus the names applied to God do not signify different ideas; and thus they are synonymous.
On the contrary, All synonyms united with each other are redundant, as when we say, "vesture clothing." Therefore if all names applied to God are synonymous, we cannot properly say "good God" or the like, and yet it is written, "O most mighty, great and powerful, the Lord of hosts is Thy name" (Jeremiah 32:18).
I answer that, These names spoken of God are not synonymous. This would be easy to understand, if we said that these names are used to remove, or to express the relation of cause to creatures; for thus it would follow that there are different ideas as regards the diverse things denied of God, or as regards diverse effects connoted. But even according to what was said above (Article 2), that these names signify the divine substance, although in an imperfect manner, it is also clear from what has been said (1,2) that they have diverse meanings. For the idea signified by the name is the conception in the intellect of the thing signified by the name. But our intellect, since it knows God from creatures, in order to understand God, forms conceptions proportional to the perfections flowing from God to creatures, which perfections pre-exist in God unitedly and simply, whereas in creatures they are received and divided and multiplied. As therefore, to the different perfections of creatures, there corresponds one simple principle represented by different perfections of creatures in a various and manifold manner, so also to the various and multiplied conceptions of our intellect, there corresponds one altogether simple principle, according to these conceptions, imperfectly understood. Therefore although the names applied to God signify one thing, still because they signify that under many and different aspects, they are not synonymous.
Thus appears the solution of the First Objection, since synonymous terms signify one thing under one aspect; for words which signify different aspects of one things, do not signify primarily and absolutely one thing; because the term only signifies the thing through the medium of the intellectual conception, as was said above.
Reply to Objection 2. The many aspects of these names are not empty and vain, for there corresponds to all of them one simple reality represented by them in a manifold and imperfect manner.
Reply to Objection 3. The perfect unity of God requires that what are manifold and divided in others should exist in Him simply and unitedly. Thus it comes about that He is one in reality, and yet multiple in idea, because our intellect apprehends Him in a manifold manner, as things represent Him.
Source: Summa Theologica (New Advent)