master-key

n (also `pass key) key made to open many different locks, each also opened by a separate key 万能钥匙.

mass media, mass-produce, Massachusetts, massacre, massage, masseur, massif, massive, massively, massiveness, massless, mast, mast-head, mastectomy, mastemaster, master, master class, Master of Ceremonies, master sergeant, Master's degree (also Master's), master-stroke, masterful, masterfully, masterly, mastermind, masterpiece, mastery, mastic, masticate, mastication, mastiff, mastitis, mastodon, mastoid, mastoiditis, masturbate, masturbation, masturbatory, mat, matador,