The Dark Divinity 3.0

[Rocl]

Eikon is just another word for primals. This was confirmed in the dev chat.

Ah, so we thought until the quest myahele linked where Urianger and Unukalhai, both of which seem to know a lot more about Primals than us (specifically the latter), inform us that Eikon and Primal are similar, but distinct. In the modern day, Garleans use Eikon to refer to Primals, but the Allagans used the word Eikon to refer to a distinct type of being similar to a Primal.

EDIT: There was a second page to this thread I didn't see, sec

The best we can figure out given in-game context and Ferne's post is that all Eikons are primals but not all primals are Eikons (and even that's a stretch I wouldn't want to make yet); there isn't information enough to say much more than "Garleans call all Primals 'eikon'" and there exists some form of distinction between 'primal' and 'eikon' given Unuhalkai's dialogue, though it may be more superficial than some of us think

Unukalhai: I sought you out that I might alert you to the rising threat of the beings known as eikons. ...You are aware of the threat, you say? Ah, but I speak not of the primals, with which you are exceedingly well acquainted. It may interest you to know that the term “eikon” and the beings to which it refers precede the Garlean Empire by eras.

Unukalhai: Ah, yes. The beings the Allagans dubbed eikons. How much we have yet to learn.
Unukalhai: Precisely how they stand apart from primals we have yet to determine. If they were summoned in a similar manner, then who was responsible, and how have they managed to endure for millennia?