Definition of Buck, from Francis Grose, 1788, reprinted 1811.

Buck. A blind horse; also a gay debauchee.

A Buck of the First Head. One who in debauchery surpasses the rest of his companions, a blood or choice spirit. There are in London divers lodges or societies of Bucks, formed in imitation of the Free Masons: one was held in the Rose, in Monkwell-street, about the year 1705. The president is styled the Grand Buck. A buck sometimes signifies a cuckold.
Buck Fitch. A lecherous old fellow.
Buckeen. A bully. Irish.

(To kick the bucket. To die. Somehow I had assumed that this phrase was American).