To alternate or take turns jointly; to succeed alternately in shared responsibility or action.
Co- (together) + alternate (Latin alternare 'to do by turns'). This is a rare, technical term combining co- (shared) with alternate, suggesting mutual or reciprocal alternation.
While coalternate is barely used in modern English, it represents an elegant medieval concept of how power should work—not as total dominance, but as shared turns!
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