In the context of protecting or guarding, some antonyms for the word "defend" include surrender, abandon, expose, neglect, and betray. Surrender is to give up, cease resistance, or acknowledge defeat, which is the opposite of defending oneself or others. Abandon is to desert or leave something unprotected, the opposite of defending or protecting something or someone. Expose means to leave something or someone vulnerable, the opposite of defending them. Neglect is to fail to take care of something or someone, the opposite of defending or guarding them. Betray means to deceive or expose someone or something that was protected, the opposite of defending or standing by them.