To lose some of one's skill in a particular area. This phrase can also be applied derisively to men who appear to have lost their virility, especially after marriage. After years away from the sport, she's half the swimmer she used to be—I doubt she'll place in the upcoming meet. A: "Can you believe that Joe is out shopping with his wife right now, instead of watching the game with us?" B: "Ever since he got married, he's half the man he used to be."