1. To play or tinker with something, often in an aimless manner. Hey, don't fool around with the thermostat—it needs to stay at 68 degrees. Grandpa's still fooling around with that old radio, but I doubt he'll get it to work again.

2. To engage in aimless recreation or frivolous time-wasting with someone or something. Quit fooling around with the dog and work on your book report already!

3. To have a casual sexual relationship with someone. I can't believe you're still fooling around with Betsy. Why don't you guys try actually dating?