探索

explore; probe; search; plumb; quest; grope; delve into; exploration; enquiry; research; exploratory

秘密

secret; confidentiality; secrecy; mystery; stealth; covert; confidence; confidential; private; privy; underhand; underground; undercover; quiet; clandestine; secure; sneaky; arcane; stealthy; surreptitious; subterranean; hush-hush; ulterior; backstreet; backdoor; back-room; closed-door; cloak-and-dagger; hole-and-corner; behind-the-scenes; secretly; backstage; inwardly; crypto-; in secret; in camera; under wraps; under the counter; on the quiet; on the downlow; on the side; on the sly; behind the scenes; behind closed doors