秘密 (mì mì) means a secret or secret (adjective). 秘 means hidden or secret and 密 means close, dense, or confidential. Together they form the standard word for a secret. Common phrases: 告诉秘密 (tell a secret), 保守秘密 (keep a secret), 揭露秘密 (reveal a secret), 秘密任务 (secret mission). As an adjective 秘密 can precede nouns: 秘密会议 (secret meeting), 秘密档案 (classified files). The antonym is 公开 (gōng kāi, public/open).