10 Consider the other recorded instances in which this name was given by favour or assumed. To Moses it was said, I have made you a god to Pharaoh. Does not this addition, to Pharaoh, account for the title? Did God impart to Moses the Divine nature? Did He not rather make Moses a god in the sight of Pharaoh, who was to be smitten with terror when Moses' serpent swallowed the magic serpents and returned into a rod, when he drove back the venomous flies which he had called forth, when he stayed the hail by the same power wherewith he had summoned it, and made the locusts depart by the same might which had brought them; when in the wonders that he wrought the magicians saw the finger of God?
That was the sense in which Moses was appointed to be god to Pharaoh; he was feared and entreated, he chastised and healed. It is one thing to be appointed a god; it is another thing to be God. He was made a god to Pharaoh; he had not that nature and that name wherein God consists. I call to mind another instance of the name being given as a title; that where it is written, I have said, You are gods. But this is obviously the granting of a favour. I have said proves that it is no definition, but only a description by One Who chooses to speak thus.
A definition gives us knowledge of the object defined; a description depends on the arbitrary will of the speaker. When a speaker is manifestly conferring a title, that title has its origin only in the speaker's words, not in the thing itself. The title is not the name which expresses its nature and kind.
Source: On the Trinity (New Advent)