God Defines...

"He's a nice guy." In other words, this man is considerate enough to be considered "nice". His character doesn't define the word nice -- he is described by the word.
"God is good." In other words, God's actions, words, and thoughts toward us are kind and loving. But unlike "nice" people, who may not always be gentle or gracious, God's character is the ultimate measure of the word. God is not described by adjectives, but if accurately used, God defines the adjective.
When God is said to be good -- or love or patient or just -- He is always good because God reflects the true meaning of the word, not vice versa. Because of this if we want to know what goodness is, we don't define the word and then measure God to see if He meets the criteria, we look to God to understand the criteria and define the word.