It’s pronounced “here-eyeth” (roll the “r”) and it’s a Welsh word. It has no exact cognate in English. The best we can do is “homesickness,” but that’s like the difference between hardwood and laminate. Homesickness is hiraeth-lite.
. . .
So hiraeth is a protest. If it must be called homesickness, it’s a sickness come on—in Welsh ailments come onto you, as if hopping aboard ship—because home isn’t the place it should have been. It’s an unattainable longing for a place, a person, a figure, even a national history that may never have actually existed. To feel hiraeth is to feel a deep incompleteness and recognize it as familiar.
Dreaming in Welsh. Boy do I identify with this.