骨干
gǔ gàn · HSK 7
diaphysis
🦴 骨 (bone) + 干 (trunk/main) = bone-trunk → backbone, core member
Literally the shaft of a long bone; figuratively the backbone of an organization — its key, load-bearing members. 干 here means trunk or main part, the same 干 as in 树干 (tree trunk).
干 — pictograph of a forked weapon/shield
干 originally depicted a forked wooden weapon or shield used in ancient warfare, giving the early sense of 'to offend' or 'to oppose.' Over time it took on extended meanings like 'to concern' and 'trunk/stem.' In modern simplified Chinese it also absorbed 乾 (dry) and 幹 (to do; trunk), so one character now covers several unrelated words.