Sometimes in the Old Testament, people were called gods because they carried out the prerogatives of God - to judge, etc. For example:
Exodus 7:1 And the Lord said to Moses: Behold I have appointed thee the God of Pharaoh: and Aaron thy brother shall be thy prophet.
Exodus 21:5-6 And if the servant shall say: I love my master and my wife and children, I will not go out free: 6 His master shall bring him to the gods, and he shall be set to the door and the posts, and he shall bore his ear through with an awl: and he shall be his servant for ever.
The Psalm itself defines these as children of God:
I said ye are gods, sons of the most, all of you.
Jesus makes reference to this verse, and it is telling.
Notice that Jesus said, "I am the Son of God," and it is this, not "I am God," that they interpreted to mean He was claiming to be God himself, that is, equal with God (as the author John himself notes is what Jesus did in fact: John 5:18). So immediately we know that Jesus was, as is quite obvious from the testimony of this and all of the Gospels, using "Son of God" in a higher sense than merely an angel or adopted son of God - claiming to have "come forth from God" in a unique sense (i.e. "the Father" and "the Son" mutually imply a begotten relationship, and not an adoption relationship).
So Jesus argues that if those to whom the Word of God came (i.e. the Jews) could be called "sons of God" - and even here, the more explicit "Gods" - then how much more can the Word of God Himself be called God, who, according to the very first words in this Gospel, "[is] God?" (John 1:1) (i.e. whereas these are only called it by way of bringing attention to their divine authority, and not to their nature).
There is no reason that "elohim" (Gods) had any more semantic range than it does in English, only its range of use (such as calling judges "gods" whom we wouldn't normally call in English gods, but whom Hebrew rhetoric evidentally does).
The fact that Jesus makes an 'if these can be called, then how much more I' argument proves that it was not just a known word for some 'divine council in heaven' (which would be known and expected to be used of them) but in fact the opposite - its use was as striking as it was to us today - as is implied by the "I said you are gods" followed by an emphatic repetition-via-synonym common to Hebrew rhetoric, "sons of the Most High, all of you" - whereas, no matter who they were imagined to be, would not be gods by nature, or really divine, because "Before me there were no gods formed, neither shall there be after me" (Isaiah 43:10).