A position in an order of standing. Rank says where, never why.
Old French renc/rang (a row, a line), from Frankish, ultimately from a Germanic root meaning ring or circle; rank shares its origin with range, both descending from the same image of things set in a row.
A position in an order of standing. The root only ever describes the row, never the reason for where anything sits in it — rank says where, and leaves why to something else entirely.