Gotta give credit where it’s due: Ethan has a pretty good memory.
As it’s implied, “Elyeo” is a Keolian mispronunciation/corruption of “Elyath.” Elyeo just happens to sound like “lady of El” (을녀) in Korean, and el means a bunch of different things, including “second,” “darkness,” “tree,” etc.
Because of that, a male Elyath would probably be called Elnam, meaning “man of El,” by Keolians. The N in Elnam is silent (eaten by the L preceding it), so it would be pronounced Elam.