Crafty, cunning, shrewd, or skillfully deceptive; cleverly dishonest.
From Latin callidus (clever, cunning, crafty), possibly related to callere (to be hard, rough, or skilled). Used in English primarily in literary and formal contexts, especially in older texts.
Callid is the sophisticated word for someone who's so clever at being dishonest that you almost have to admire the skill—it's cunning without quite the moral judgment of 'deceitful.'
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