Definition of "Buck" :

noun: mature male of various mammals (especially deer or antelope)

noun: a framework for holding wood that is being sawed

noun: a gymnastic horse without pommels and with one end elongated; used lengthwise for vaulting

noun: United States author whose novels drew on her experiences as a missionary in China (1892-1973)

noun: a piece of paper money worth one dollar

verb: jump vertically, with legs stiff and back arched

"The yung filly bucked."

verb: move quickly and violently

verb: resist

"Buck the trend."

verb: to strive with determination

"John is bucking for a promotion."