noun
wrestler of grand champion quality without the title
Sumo term for a wrestler whose ability is on par with a yokozuna but who has not been promoted to that rank.
彼は無類力士と呼ばれ、横綱に匹敵する実力を持っていた。
He was called a muroi-rikishi and had ability comparable to a yokozuna.
Compound of 無類 (むるい, 'peerless, unparalleled') and 力士 (りきし, 'sumo wrestler'). The exact origin is uncertain, but it is a sumo-specific term.