n.1. Bold resistance against an opposing force or authority: engaged in acts of defiance against the regime.
2. Contemptuous disrespect for the authority of another: detected a tone of defiance in the letter.
3. Archaic A challenge, as to combat or a duel: "Violent was Mr. Weller's indignation as he was borne along; numerous were the allusions to the personal appearance and demeanour of Mr. Grummer and his companion; and valorous were the defiances to any six of the gentlemen present, in which he vented his dissatisfaction" (Charles Dickens).