vulgar slang To start acting in a strong, confident, and/or courageous manner, especially after having previously failed to do so. The phrase is short for "grow a pair of balls (testicles)," but is not exclusively applied to males. Often used as an imperative. You need to grow a pair and ask your boss for a raise already! Janet, I know you're nervous about asking Tom out on a date, but just grow a pair and give it a shot!