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
"Buck the trend."
verb: to strive with determination
"John is bucking for a promotion."