腰
こし · koshi · JLPT N3 · noun
waist
👖 月 flesh + 要 essential: the body's essential hinge, your waist
要 originally showed a person with hands on the hips and meant waist, before it came to mean essential. The flesh radical 月 was added to keep the body sense. Sound hook: koshi sounds like cushy, a cushy seat for your hips.
腰 — flesh radical 月 (肉) + 要 yào (phonetic)
A semantic-phonetic compound. The 月 (flesh) radical signals a body part, while 要 supplies the sound 'yāo'. Notably, 要 itself originally depicted a person with hands on the waist, so it once meant 'waist'; when 要 shifted to mean 'want/important', 腰 was created with the flesh radical to preserve the original sense.