busy vs hard at work

busy

verb
  • To rush somebody. 

  • To make somebody busy or active; to occupy. 

noun
  • A police officer. 

adj
  • Having a lot going on; complicated or intricate. 

  • Officious; meddling. 

  • Engaged in activity or by someone else. 

  • Crowded with business or activities; having a great deal going on. 

hard at work

prep
  • Labouring with great effort and diligence; working hard. 

How often have the words busy and hard at work occurred in a corpus of books? (source: Google Ngram Viewer )