"The question implicit in any discussion of the names of God is this: how can words or names be common to creature and God? God is wise, but 'wise' is a word that is applied to such men as Socrates. God is good, but 'good' is applied to many other things. God is just, but so is St. Joseph . . . And so on. The names of God are shared with creatures, and it is the meaning the terms have as said of creatures that provides the springboard for understanding their application to God. Names are not common to God and creature univocally or equivocally but analogically.
A univocally common name receives the very same account as said of many things. E.g 'man' said of this person and that and the other and so on. An equivocally common name is one which receives quite different and unrelated accounts as said of many things. 'Slip' as said of a place for a boat and of an item of lingerie is the same word, but there would seem to be no connection at all between these two meanings of it. An analogous name, Thomas says, is midway between these two.
The implicit question, again, is how is the same word said of God and creature? 'Wise' doesn't get exactly the same account in these two instances. For one thing, the wisdom of Socrates is a hard-earned characteristic, There was a time when he was not wise, he has lapses even in his prime, and eventually he may end up drooling out of both corners of his mouth and uttering nonsense. None of that is true of God. Why not? The basic rule is to deny of God anything that is imperfect. But of 'wise' said of Socrates entails all these imperfections, how can it be predicated of God?
By purifying it of those imperfections. By eliminating the creaturely mode of wisdom. And what is left? Wisdom. But wouldn't this be like the onion once it is completely unpeeled. What could possibly be left after we peel away the features of Socrates' wisdom? Thomas says we can indeed retain these perfections without their accompanying imperfections; indeed, we must if the word is to be applied to God. And of course God has applied the word to himself, so this is a spur to the theologian to go on. The perfection is found in God in a manner quite different from the manner it is found in creatures."
-Taken from the Introduction to Thomas Aquinas study materials found on catholicthinkers.org