外公
wàigōng · HSK 7
maternal grandfather
👴 外公 = outside + elder; mother's side counts as the outside family line
外 means outside/external and 公 is an elder male. In the traditional patrilineal system the mother's relatives sit outside the main family line, so her father is the outside grandfather. Contrast with 爷爷, the paternal grandfather.
外 — evening 夕 + divination 卜
Originally a compound of 夕 (evening) and 卜 (divination). Ancient Chinese divinations were performed in the morning; doing them at evening (夕) was considered irregular or 'outside' the norm. From this sense of deviation, 外 came to mean 'outside' or 'external'.
公 — eight 八 + private 厶
Originally an ideograph showing 八 (to divide) over 厶 (private/self), depicting the act of splitting away from selfish interest. The combination came to mean 'public' or 'fair,' the opposite of private. It later extended to senses like 'duke,' 'lord,' and 'grandfather.'