to spoil a surprise or a joke by letting someone know something that should have been kept secret.

We were trying to pretend we didn't know it was her birthday but Sam gave the game away.

• cut off your nose to spite your face
• cut out
• cut out for
• cut out for something
• cut out something
• cut own throat
• cut someone dead
• cut someone down to size
• cut someone loose
• cut someone some slack
• cut someone to the quick
• cut some slack
• cut something down to size
• cut something loose
• cut teeth
• cut teeth in
• cut teeth in something
• cut the cord
• cut the crap
• Cut the crap!
• cut the Gordian knot
• cut the ground from under feet
• cut the ground from under someone feet
• cut the ground from under someone's feet
• cut the umbilical cord