buck 1 
(bŭk)
(bŭk)n.
1.
a. A male deer.
b. The male of various other mammals, such as antelopes, kangaroos, mice, or rabbits.
c. Antelope considered as a group: a herd of buck.
2.
a. A robust or high-spirited young man.
b. A fop.
3. Offensive A Native American or black man.
4. An act or instance of bucking: a horse that unseated its rider on the first buck.
5.
a. Buckskin.
b. bucks Buckskin breeches or shoes.
v. bucked, buck·ing, bucks
v.intr.
1. To leap upward arching the back: The horse bucked in fright.
2. To charge with the head lowered; butt.
3. To make sudden jerky movements; jolt: The motor bucked and lurched before it finally ran smoothly.
4. To resist stubbornly and obstinately; balk.
5. Informal To strive with determination: bucking for a promotion.
v.tr.
1. To throw or toss by bucking: buck off a rider; bucked the packsaddle off its back.
2. To oppose directly and stubbornly; go against: "Los Angeles County, the most populous county in the country, is bucking the trend" (American Demographics).
3. Football To charge into (an opponent's line) carrying the ball.
4. To butt against with the head.
adj.
Phrasal Verb: Of the lowest rank in a specified military category: a buck private; a buck sergeant.
buck up
To summon one's courage or spirits; hearten: My friends tried to buck me up after I lost the contest.
[Middle English bukke, from Old English buc, male deer, and bucca, male goat.]
bucker n.