tip one's hand

tip (one's) hand

To reveal one's intentions, plans, secrets, or resources. An allusion to letting someone else see the cards one is currently holding (one's "hand"). The foreign leader has definitely tipped his hand when it comes to his country's position in the negotiations. Remember not to tip your hand when you go into the meeting.
See also: hand, tip

tip one's hand

Accidentally reveal one's intentions, as in He avoided any comments on birthdays for fear of tipping his hand about the surprise party . This idiom probably alludes to holding one's hand in such a way that others can see the cards one is holding. [Colloquial; early 1900s]
See also: hand, tip