Knuckle under and Knuckle down

Knuckle under verb - To cease resistance (as to another's arguments, demands, or control).

Knuckle down and knuckle under are semantically related. In some cases you can use "Knuckle down" instead a verb "Knuckle under".

Knuckle down verb - Work very hard, like a slave.

Knuckle under and knuckle down are semantically related. Sometimes you can use "Knuckle under" instead a verb "Knuckle down".