It’s a determiner
“a negative answer or decision”
It’s an abbreviation for North and Number.
And No1, is the symbol for the chemical element nobelium.
Here’s a chart of it’s use over the years.
The opposite of “Yes”
“a denial or refusal”
To turn something down is to tell it “no”.
Nay, nope, negative, absolutely not.
No way José.
Nix, never, by no means.