The word “hat” has some interesting idioms (modismos).
Here they are:
• Mr. Sanchez should hang up his hat (= jubilarse)
• That is old hat (eso no es nada nuevo).
• We should pass around the hat for Zapatero (debiéramos pasar el platillo para…).
• Mr. Más talks through his hat (Mr. Más dice disparates).
• Keep it under your hat (de esto no digas nada).
• Mrs. Merkel is wearing two hats (…esta ejerciendo un doble papel).
Many moons ago (hace muchas lunas) in England people used to wear a hat, a hat that was specific to their job. So a lawyer (abogado) would wear one type of hat, and a banker (banquero) another type. Therefore, when someone hung up his hat (colgó un sombrero) it meant that he was retiring (de jubilación).
The lining of a hat (forro) was used to hide (or keep safe) money and documents, hence (por lo tanto, o de ahí) “keep it under your hat”.