Elianath was one of many names and words used in the incantation "Enamorath! Emmoreth! Ba'alSetElianath!" which was used to cast spells from the Darkhold.[1]
Notes
The exact nature of Elianath is unknown and may not be a character, but an object or place. However, it is assumed since the spell invokes Ba'al and Set as well that Elianath is a person.