Region: US | Usage example: He kept his ace in the hole—the unpublished research—until the debate started.

Ace in the hole

Meaning

A hidden advantage kept in reserve until it's needed.

Popular in contexts where strategy or competition is discussed.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

From stud poker, where an 'ace' dealt face down was a secret asset.

Spread through gambling jargon into general English by the early 1900s.