Keep it under your hat

Meaning

Keep something secret.

Usage

Used when asking someone to keep confidence.

Origin & History

Origins and dates here are approximate summaries. Many idioms have disputed or unknown origins, and not every date has been checked against a historical dictionary, so treat specific dates and stories as a starting point rather than a citation.

Hats once stored private notes and valuables, symbolizing discretion.

The phrase appears in 19th-century etiquette guides.