Questioner
Why is it called a Nahel bond?
Brandon Sanderson
That is a word in Rosharan. I'm not sure what it meant in 2002, but it basically just means "the bond to divinity." I'm not sure what the 2002 version of the linguistics played out as. I actually just called it Nahel in the original draft. I added "bond" in as I prepared this [Way of Kings Prime excerpt] for reading so it would make more sense to people.
Skyward Chicago signing (Nov. 16, 2018)
Questioner
In the reading that you did, the Nahel bond, has it changed?
Brandon Sanderson
Yes. So, spren were added, and things like that. What he had would still be called a Nahel bond. A Nahel bond in the original definition means bond to divinity, but that's come to encompass a lot more in the cosmere, any time you're bonding with-- the bond between a soul and Investiture. But in the original version, it was more only with a Shard of Adonalsium or something like that.
Skyward Houston signing (Nov. 19, 2018)
Good theory though