The term "looselipped" is often used to describe someone who talks too much, especially about sensitive or confidential matters. Antonyms for looselipped could include "taciturn," meaning reserved or silent, and "guarded," indicating caution in what is said. "Secretive" may also be an antonym, suggesting a reluctance or inability to discuss personal or private information. Additionally, "discreet" embodies the idea of keeping something confidential, without the need to gossip or share details. Other antonyms may include "reserved," "reticent," "hushed," and "silent." All of these words suggest a level of discretion and restraint that is the opposite of being looselipped.