great on (something)

informal

1. Knowledgeable about some topic or thing. Yeah, she did her thesis on postmodernism, but she's great on Victorian lit too—she's actually quite the Tennyson buff. My mother is great on cooking and can make just about any dish. I had no idea Maria was great on real estate trends in the area!

2. Passionate or enthusiastic about some topic or thing. I didn't realize Uncle Joe was so great on cars—he just went on a 20-minute monologue about the joys of owning a Corvette! My friends are great on the Roboformers film franchise too, which has led to some spirited debates between all of us! Uncle Ned is great on politics, so don't get him started unless you want to hear about the state of the Senate for an hour.