Knuckle under vs knuckle down

Knuckle under and knuckle down are two idioms that are similar but have very different meanings. An idiom is a word, group of words or phrase that has a figurative meaning that is not easily deduced from its literal meaning. We will look at the difference between knuckle under and knuckle down, where the terms […]
from Grammarist
http://grammarist.com/idiom/knuckle-under-vs-knuckle-down/