“To unbosom” means “to disclose information,” especially secrets. “Unbosom” belongs to a collection of words that incorporate “bosom,” which means “breast, womb, surface, or ship’s hold.” “Embosom” means “to shelter closely,” and “disbosom” means “to disclose a secret,” just like “unbosom.” The Old English root word, “bosm,” comes from the West Germanic “bōsmaz.” There’s an idiom about keeping secrets — “keep your cards close to your chest (or vest)” — that seems like it could be related to the word “unbosom,” but the origin is in poker and keeping the faces of the cards protected from spying eyes.