And your etymology is as bad as the rest of it.
"Sir" is a contraction of "sire", and "sire" is a contraction of seior/ senior: one who is older (and incidentally also relates to (my) father).
(And can be seen in the French "sieur"/ "monsieur").
That still poses no contradiction in terms. So...Yes, the term "my father" fits quite nicely.
Also "sire" speaks of the person "whom one is begotten by" or sired.
Did the word "Sir" once imply the title of "Great Serpent"?
I don't know that for sure, but I do know this much is true...
The serpent "host" that Satan used to beguile Eve was the "man" that fathered Cain, not Adam. It was not a reptile.
This created the two races (Adamic and Cainite) that mixed again as mentioned in Gen. 6, but in the opposite way of what is commonly taught.
Most theologians all the way back to Josephus teach the daughters of men were Adamic and the sons of God that took them as wives were fallen angels who "pressed into" or created for themselves male bodies. It may seem to be a fine line, but the opposite is actually the truth.
The sons of God were of the Adamic linage through Seth, who disobeyed God in marrying the Cainite daughters of the linage of serpent "hosts".
Because the serpent was a man, these Cainite women were called the daughters of men. Adam was of God. His offspring were the sons of God.
These were the "souls in prison that repented not in the days of the preaching of Noah", that Jesus preached to when He was dead.
It was by this that they polluted the pure bloodline of God passed down from Adam through Seth.
That is what corrupted the way of all flesh on the earth, and brought about the destruction.
Two different groups with different origins combined to make the human race as it is today.
When Satan tempted Jesus he showed Him all the kingdoms of the world in a moment of time.
Then he said; "All this power will I give thee, and the glory of them: for that is delivered unto me; and to whomsoever I will I give it.
If thou therefore wilt worship me, all shall be thine." Jesus didn't deny the world was Satan's to offer at that time.
The kingdoms of this world have belonged to the serpent's linage since the time they were "delivered unto" him.
By His statement "to whomsoever I will I give it" we can deduct He has had the right to chose who would be it's ruling classes.
Now to answer the question; "Is it true that the term "Sir" was once associated with "Great Serpent"?
After reading this I'll let you be the judge, but I'd say there was a real good possibility.