What is the meaning of Buck_up?

Cheer up; take courage; take heart.

Hurry up; make haste.

To become encouraged, reinvigorated, or cheerful; to summon one's courage or spirits; to pluck up courage.

To encourage; to hearten.

To do better.

To dress oneself up smartly; compare (obsolete) buck ("a fop, dandy")

To pass on to higher authority for resolution. See also pass the buck.

To hurry up.

To hit or fight (someone).

Source: wiktionary.org