The phrase "most unbosom" means to be extremely honest or open with someone, often revealing personal feelings or secrets. Antonyms for this phrase include words like dissemble, conceal, hide, or cover-up, which imply a sense of secrecy, dishonesty, or insincerity. If someone is not "most unbosoming," they may be guarded, reserved, or cautious with their words. Alternatively, they may actively be disguising, evading, or avoiding the truth or their true feelings. Antonyms for "most unbosom" can represent a lack of trust, a desire for privacy, or a fear of vulnerability, depending on the context and situation.