hard at

hard at (something)

Working diligently on something. 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 work. We've been hard at this research for the last three years.
See also: hard
Farlex Dictionary of Idioms.

hard at (something)

 and hard at doing something
working hard at something. Tom's busy. He's hard at work on the lawn.
See also: hard
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • hard at (something)
  • hard at it
  • plug away
  • plug away (at something)
  • peg away
  • peg away (at something)
  • peg away at
  • nose to the grindstone
  • dally over
  • dally over (something)
References in classic literature
I told him, that as he worked so hard at bogging, he required thick boots and stout clothing, which yet were soon soiled and worn out, but I wore light shoes and thin clothing, which cost not half so much, though he might think that I was dressed like a gentleman (which, however, was not the case), and in an hour or two, without labor, but as a recreation, I could, if I wished, catch as many fish as I should want for two days, or earn enough money to support me a week.
Walden & on the Duty of Civil Disobedience
A little hard-headed, Ripstone pippin-faced man, was conversing with a fat old gentleman in one corner; and two or three more old gentlemen, and two or three more old ladies, sat bolt upright and motionless on their chairs, staring very hard at Mr.
The Posthumous Papers Of The Pickwick Club
I don't know how master brought her to the house, being hard at work at the time.
The Woman in White
But we had been hard at the work of scholarly ethics since breakfast, and the sudden arrival of coffee and dessert made me think it was time to shift gears into something more playful.
Public morality from a private eye