Definição e Significado de "[keep] {sth} under {one's} hat"

What is the origin of the idiom "keep something under one's hat" and when to use it?

The idiom "keep something under one's hat" has its origins in the imagery of concealing information beneath one's hat to prevent others from seeing or knowing about it. The phrase emerged in the late 19th century and is associated with the practice of secretiveness or discretion. The expression is now used to suggest the idea of holding onto a piece of information privately, similar to hiding it beneath one's hat, and has since become a colloquial way to advise someone to keep a secret or to discreetly manage information.