The son of one's child.
Compound of 'grand' (meaning great or principal) and 'son'. 'Grand' in family relationships comes from Old French 'grand' meaning great, indicating a generation removed from direct parent-child relationship.
The 'grand' in grandson doesn't mean large or impressive - it's a linguistic artifact from French family terminology where 'grand' indicated important family relationships one generation removed, like a great noble title passed down.
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