- to summon the courage to do something
- to become encouraged or cheerful after a tragic incident
- to get over something unpleasant
- After losing the first place position to Martha, everyone heard Mary's mother tell her to buck up.
- People should learn to buck up after encountering any major issues as this is the only way they can succeed.
- Matthew was told to buck up and resit the exams next year.
- Sometimes it can be difficult to buck up and continue after suffering a huge loss.
- Naomi found it easy to buck up even after she failed out of medical school.
- After the devastating fire that claimed the lives of her entire family, Alicia has managed to buck up and put her life back together.
The origin of the phrase comes from 19th century Great Britain, derived from those bucks or dandies who were regarded as the acme of snappy dressing in the Regency period. (In its turn, that word came from buck in the sense of the animal, and had a slightly older meaning still that suggested male gaiety or spirit, with unsubtle suggestions of rutting deer.)
In its dandified sense buck up first meant to dress smartly, for a man to get out of those comfortable old clothes and into something drop-dead gorgeous. Since to do so was often a fillip to the spirit, the phrase shifted sometime around the 1880s to its modern meaning.
It seems to have been public school slang to start with, probably from Winchester College, and rather stiff-upper-lip British. It could suggest that the person being addressed should stop acting like a wuss, ninny, or coward, as here from Edith Nesbit's The Wouldbegoods of 1901:
"Be a man! Buck up!", and was something of a cliché at one time in stories of Englishmen abroad bravely facing adversity.
From the early years of the 20th century, it could also be an injunction on somebody to get a move on or hurry up; here's an example, from D H Lawrence's Sons and Lovers of 1913:
"Half-past eight!" he said. "We'd better buck up"
It derives directly from the word 'buck,' which has the same meaning as a stag. The stag is a majestic animal, and so to buck up initially meant to look smarter or tidy up one's appearance. Later, it evolved to being used to mean to cheer up or to just move on after a bad experience.