i-adjective
firm; persevering; resilient
Literally 'strong-waisted', used figuratively for a person's character: stubbornly persistent, unyielding, or resilient under pressure. Often implies a tough, unbreakable spirit.
See also: 腰が強い
彼は腰の強い交渉相手だ。
He is a tough, unyielding negotiator.
あの選手は腰の強いプレーで知られている。
That player is known for his resilient, hard-to-break style of play.