外婆
wàipó · HSK 7
maternal grandmother
👵 外 outside + 婆 old woman: the maternal (outside-the-paternal-line) grandmother
外 wài means outside; 婆 pó means old woman or granny. In the traditional family line, the mother's parents counted as outside the paternal household, so 外婆 marks grandma on the mother's side. Contrast 奶奶 for the paternal grandmother.
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'.