 
		
		Definition of buck:
		
								
				"the police caught me driving a buck-forty on the freeway."
			
			
	
		
		
		(v) :
		
		of a 
horse: to rise sharply up on its 
hind legs; of a 
horse: to leap upward arching its back
		
 
								
				"1848: At the same time we got speared, the horses got speared too, and jumped and bucked all about &mdash"