if a horse bucks, it kicks its back feet into the air, or jumps with all four feet off the ground
to suddenly move up and down or backwards and forwards in an uncontrolled way:
The plane bucked sharply.
to oppose something in a direct way:
He was a rebel who bucked the system (=opposed rules or authority).
Unemployment in the area has bucked the trend by falling over the last month.
Initially he had bucked against her restraints.
to make someone feel more happy, confident, or healthy:
make somebody happier[transitive]
He was bucked by the success he'd had.
She gave me a tonic which bucked me a little.
buck for somethingphrasal verb
He's bucking for promotion.
buck upphrasal verb
to become happier or to make someone happier:
Come on, buck up, things aren't that bad!
buck somebody ↔ up
You need something to buck you up.
2 British English old-fashioned
used to tell someone to hurry up:
Buck up, John! We'll be late.
to improve, or to make something improve:
It'll be a long time before the situation starts to buck up.
buck something ↔ up
a company that is looking to buck up its networking capabilities
4 British English informal
used to tell someone to improve their behaviour or attitude