be hard at it

To be doing something with much effort. I've been hard at it for months, and I'm still not happy with the plot of my novel. I've been trying to get him to do his book report all day, so I'm glad to see that he's finally hard at it. A: "Dad's still trying to fix that old engine?" B: "Oh yes, he's been hard at it all week."

be hard ˈat it

be working hard: She’s been hard at it all day. ♢ When I left at six, he was still hard at it. OPPOSITE: take it/things easy