Sentence:  Swankey of the Body Guard himself, that dangerous youth, and the greatest <WSD>buck</WSD> of all the Indian army now on leave, was one day discovered by Major Dobbin tête-à-tête with Amelia, and describing the sport of pig-sticking to her with great humour and eloquence ... 
Meaning of the word marked with <WSD> tags:  A young buck; an adventurous, impetuous, dashing, or high-spirited young man.