Ruling jointly or together; one who rules jointly with another.
From 'co-' (together) + 'regnant' (from Latin 'regnans' ruling, from 'regnare' to rule, from 'regnum' kingdom). The term combines Latin royal terminology.
The word 'regnant' itself is fascinating—it means 'currently ruling,' so Queen Victoria was the 'reigning' or 'regnant' monarch, and if two people shared that power, they'd both be 'coregnant,' making this a word that appears almost exclusively in formal historical contexts.
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