Emily Dickinson Lexicon

DE-FY', v.t. [Fr. defier; de, des, from, and fier, to trust; It. sfidare; Sp. desafiar; des and fiar; Port. id.; Arm. difyal; Low L. diffidare, and diffiduciare, from fido, to trust. See Faith. The word diffidare seems originally to have signified, to dissolve the bond of allegiance, as between the lord and his vassal; opposed to affidare. Spelman, ad voc. Hence it came to be used for the denunciation of enmity and of war. Hence, to challenge. If we understand defier to signify to distrust, then to defy is to call in question the courage of another, according to the popular phrase, “you dare not fight me.”]

1. To dare; to provoke to combat or strife, by appealing to the courage of another; to invite one to contest; to challenge; as, Goliath defied the armies of Israel.
2. To dare; to brave; to offer to hazard a conflict by manifesting a contempt of opposition, attack or hostile force; as, to defy the arguments of an opponent; to defy the power of the magistrate. Were we to abolish the common law, it would rise triumphant above its own ruins, deriding and defying, its impotent enemies. – Duponceau.
3. To challenge to say or do any thing.