Tip One's Hand Meaning

(idiomatic) To inadvertently reveal any secret, particularly a secret that puts one at an advantage or disadvantage.

Example: In card playing, to accidentally reveal one's cards or hand.
1952 March 10, "Cause for Alarm," Time:
  In Montreal, a 23-year-old pyromaniac tipped his hand by rushing into the fire station a few minutes before the gong rang, shouting: "Where's the fire?"
2004 March 4, Randal C. Archibold, "As Edwards’s Race Ends, Talk of No. 2 Spot on Ticket," New York Times (retrieved 20 Apr 2009):
  In a nearly 13-minute address, he did not tip his hand about what he might do next.