keep under one's hat

1. 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]

Related Words

• conceal 
• deduct 
• deny 
• detain 
• hide 
• keep 
• refuse 
• resist 
• retain 
• suppress