骨 is a compound ideograph: 冎 (a stylized depiction of bones — recognizable as skull and vertebrae stacked together) on top, plus 月 (the flesh radical) below. The combination reads as "the hard structure embedded within flesh" — bone. As a radical, 骨 itself anchors a small but vivid family: 髄 (suǐ, marrow), 骸 (hái, skeleton / corpse), and historically 體 (the traditional form of "body," etymologically "the abundance of bones"). Bones are conceived in Chinese tradition as the body's essential framework.

Korean reading "gol." Saturates anatomical and metaphorical vocabulary: 骨格 (golgyeok, skeleton / framework — used both anatomically and architecturally), 骨折 (goljeol, bone fracture), 骨髓 (golsu, bone marrow), 骨董品 (goldongpum, antique — literally "bone-collected piece," referring to objects so old their substance is bone-like), 遺骨 (yugol, remains / ashes of the deceased), 氣骨 (gigol, "spirit-bones" = backbone / strength of character). The metaphorical extension "bone → essential framework / strength of character" runs across all CJK languages.

Mandarin gǔ, 3rd tone. 骨 (gǔ, bone), 骨头 (gǔtou, "bone-head" = bone — colloquial), 骨骼 (gǔgé, skeleton), 骨干 (gǔgàn, "bone-stem" = backbone / core member of an organization), 骨折 (gǔzhé, fracture). The metaphor 骨干 ("bone-stem" = key personnel / structural backbone) is identical in feel to Korean 골격 / 기간.

Japanese on-reading コツ (kotsu) — 骨折 (kossetsu, fracture, with the doubled consonant from sandhi), 骨格 (kokkaku, skeleton), 骨髄 (kotsuzui, bone marrow), 遺骨 (ikotsu, cremated remains — central to Japanese funerary practice; the bones picked up with chopsticks after cremation are called 骨上げ kotsuage). Kun-reading ほね (hone, bone) — 骨 (hone), 骨組み (honegumi, framework / structure), and the lovely idiom 骨折る (honeoru, "to break one's bones" = to take great pains / work hard at something). 骨を惜しまない (hone o oshimanai, "not to spare one's bones") means "to spare no effort." Japanese has a particular fondness for using 骨 as the metaphor for diligent labor.

Memory aid: 冎 (bone shape on top) plus 月 (flesh below) — the hard structure inside the soft tissue.