2
general::
noun ADJ. bony | bleeding, bloodied, bruised, grazed, swollen VERB + KNUCKLE crack He rubbed his hands together, cracking his knuckles as he tried to control his anger. | bruise, graze, scrape, skin KNUCKLE + NOUN bone PHRASES rap sb on/over the knuckles (figurative) The Assistant Manager was rapped over the knuckles for criticizing the company in the press.
Oxford Collocations Dictionary
3
general::
knuckle down
informal
to start working or studying hard
• You're going to have to really knuckle down ( to your work) if you want to pass your exams., knuckle under
informal
to accept someone's power over you and do what they tell you to do
Cambridge-Phrasal Verbs