Wiktionary
arch rival
n. (alternative form of archrival English)
Usage examples of "arch rival".
Alone down below, he and his arch rival would have had the time to settle things once and for all, but now the prospect of getting Drizzt alone for a fight seemed remote and moving farther away with every second.
Evans was want to describe his arch rival, the chief architect, as 'a cocky little bastard who thinks he knows it all,' the exception being that he knew nothing about landscaping.
The stout party in - white duck pants was Laird, coach of the Knickerbockers and Connaught's arch rival.
After Prince Yder allowed the seraph of an arch rival to not only discover the Karsestone's role and location, but to come so close to stealing it, I am sure she will find a safer place to hide it.