keep under one's hat

Preserve the secrecy of something, as in I'll tell you about it if you promise to keep it under your hat. This usage alludes to hiding a secret in one's head, covered by a hat. [Late 1800s]

Common Names:

Name	Pronounced	Usage
Valentin	VAH-len-teen (German), vah-lyen-TEEN (Russian), vah-leen-TEEN (Russian)	French, Romanian, German, Danish, Swedish, Norwegian, Czech, Russian, Bulgarian, Slovene, Croatian,
Yoana	-	Bulgarian
Alwyn	-	Welsh
Jaasau	-	Biblical
Hadewych	HAH-də-veekh, HAH-də-weekh	Dutch
Careen	kə-REEN	English (Rare)