The term "loose-lipped" is used to describe someone who is talkative or prone to revealing secrets. Its antonyms, on the other hand, describe someone who is steadfast and guarded with their words. Some possible opposite words for "loose-lipped" are tight-lipped, reserved, discreet, cautious, and reticent. These words imply a sense of control over one's speech, and a reluctance to share personal information or opinions. Someone who is tight-lipped may come across as mysterious or uncommunicative, but they are also respected for their ability to keep confidences and maintain privacy.