Okay, so let's test out this theory. Let's look at other passages that speak of the nacash (nahash) and see if your theory holds up.
Gen. 49:17 Dan shall be a serpent by the way,
A viper by the path,
That bites the horses heels
So that its rider shall fall backward.
Ex. 4:3 And He said, Cast it on the ground. So he cast it on the ground, and it became a serpent; and Moses fled from it.
Num. 21:6 So the LORD sent fiery serpents among the people, and they bit the people; and many of the people of Israel died.
Num. 21:7 Therefore the people came to Moses, and said, We have sinned, for we have spoken against the LORD and against you; pray to the LORD that He take away the serpents from us. So Moses prayed for the people.
Num. 21:9 So Moses made a bronze serpent, and put it on a pole; and so it was, if a serpent had bitten anyone, when he looked at the bronze serpent, he lived.
Deut. 8:15 who led you through that great and terrible wilderness, in which were fiery serpents and scorpions and thirsty land where there was no water; who brought water for you out of the flinty rock;
2Kings 18:4 He removed the high places and broke the sacred pillars, cut down the wooden image and broke in pieces the bronze serpent that Moses had made; for until those days the children of Israel burned incense to it, and called it Nehushtan.
Is. 65:25 The wolf and the lamb shall feed together,
The lion shall eat straw like the ox,
And dust shall be the serpents food.
They shall not hurt nor destroy in all My holy mountain,
Says the LORD.
Jer. 8:17 For behold, I will send serpents among you,
Vipers which cannot be charmed,
And they shall bite you, says the LORD.
Amos 5:19 It will be as though a man fled from a lion,
And a bear met him!
Or as though he went into the house,
Leaned his hand on the wall,
And a serpent bit him!
Amos 9:3 And though they hide themselves on top of Carmel,
From there I will search and take them;
Though they hide from My sight at the bottom of the sea,
From there I will command the serpent, and it shall bite them;
Mic. 7:17 They shall lick the dust like a serpent;
They shall crawl from their holes like snakes of the earth.
They shall be afraid of the LORD our God,
And shall fear because of You.
Psa. 58:4 Their poison is like the poison of a serpent;
They are like the deaf cobra that stops its ear,
Psa. 140:3 They sharpen their tongues like a serpent;
The poison of asps is under their lips.
Selah
Prov. 23:32 At the last it bites like a serpent,
And stings like a viper.
Prov. 30:19 The way of an eagle in the air,
The way of a serpent on a rock,
The way of a ship in the midst of the sea,
And the way of a man with a virgin.
Eccl. 10:8 He who digs a pit will fall into it,
And whoever breaks through a wall will be bitten by a serpent.
Eccl. 10:11 A serpent may bite when it is not charmed;
The babbler is no different.
In all these verse above, your definition does not work. All of these are the same root word,
nachash. And yet if you put "one who speaks enchantments" instead of serpent, the passages won't make any sense. Notice all the parallelisms with other names for snakes. In english we also have multiple names for snakes, serpents vipers cobras, asps, etc. The use of nachash with all these other terms shows the hebrews understood it as a parallel term.
Now it is true that the hebrew uses the word
nachash to describe enchantment or sorcery based on the original snake's behavior. An ultra literal translation might be snakery or serpentry which would be understood is sorcery to the hebrew reader. But since in english we don't have such a derived term, we translate it as sorcery or enchantment. But that doesn't erase the normal usage of that word, it merely adds to its meaning in certain contexts. But you look at the verses above, you see that the only valid translation in those cases is
serpent or
snake.
Now we do sometimes use the term
snake in english to describe a swindler or sometimes an unfaithful cheating spouse, etc. So even in english we'll use the term snake in a non-literal meaning. But that doesn't negate the normal usage of the term to describe an animal that goes about on its belly.