The daughter of your son or daughter; your grandchild who is female.
From 'grand-' (great, from Latin 'grandis') + 'daughter' (from Old English 'dohtor'). Entered English as family relationships became more specifically labeled.
Languages differ wildly in how they name family—English uses 'grand' (great) for both 'grandmother' and 'granddaughter,' but some languages call grandparents by completely different roots!
Complete word intelligence in one call. Free tier — 50 lookups/day.