Definitions of buck:

• noun:   mature male of various mammals (especially deer or antelope)
• noun:   United States author whose novels drew on her experiences as a missionary in China (1892-1973)
• noun:   a gymnastic horse without pommels and with one end elongated; used lengthwise for vaulting
• noun:   a framework for holding wood that is being sawed
• noun:   a piece of paper money worth one dollar
• verb:   resist

  Example: "Buck the trend"

• verb:   to strive with determination

  Example: "John is bucking for a promotion"

• verb:   jump vertically, with legs stiff and back arched

  Example: "The yung filly bucked"

• verb:   move quickly and violently
• adjective:   of the lowest rank in a category

  Example: "A buck private"

• name:  A surname (common: 1 in 6250 families; popularity rank in the U.S.: #755)
• name:  A male given name (rare: 1 in 25000 males; popularity rank in the U.S.: #1205)