Anatomical term for the large pelvic bone. In everyday conversation, 骨盤 (こつばん) is more common for the pelvis as a whole.
I went to an orthopedist because the area around my hipbone hurts.
fortitude; perseverance; backbone
Figurative use likening mental toughness to a strong hipbone. Often appears in expressions like 腰骨を据える (to settle down to something with determination) or 腰骨が強い (to have a strong will).
彼は腰骨が強いから、どんな困難にも負けない。
He has a strong backbone, so he won't be defeated by any hardship.
腰骨を据えて仕事に取り組む。
I settle down to work with determination.
Compound of 腰 (こし, 'lower back, hips') and 骨 (ほね, 'bone'). The figurative sense comes from the idea that a strong hipbone supports the body, symbolizing mental strength and perseverance.