Fig.: to reveal, often unintentionally, one's intentions, plans, secrets, or resources

“She needs to show stronger leadership, but so far she hasn't even revealed in what direction she really wants to move.” Events appear to be forcing Mrs. Merkel to tip her hand. (The New York Times)

“Deve mostrare una leadership più forte, ma finora non ha nemmeno fatto capire in che direzione intenda muoversi.” Sembra che gli eventi forzino la Merkel a scoprire le sue carte. (The New York Times)

I think you shouldn't have tipped your hand so soon at the negotiating table. You should have let them reveal their intentions a bit first

Secondo me non avresti dovuto scoprire le tue carte così presto al tavolo delle trattative; avresti dovuto lasciare che loro si sbilanciassero un po' prima

I knew something weird was going on. Your principal tipped his hand when he called me on the phone, told me this bizarre story and asked me to see him at school

Sapevo che c'era qualcosa di strano. Il tuo preside ha involontariamente scoperto le sue carte quando mi ha telefonato raccontandomi una storia bislacca e mi ha convocato a scuola per parlarmi

In card playing, the cards you are currently holding are called a “hand.” You should always keep your cards straight up, because if you “tip your hand” (incline or tilt your cards), your opponents could see what you have