Here's another definition that may have been overlooked: the last part of a single-thong lash whip, such as a bullwhip or stockwhip (as opposed to a multi-thong, such as a Cat-O'-Nine-Tails) is formed of a thin twisted strand of nylon string about 6 inches long, and is called the "cracker" because that's the part of the whip that actually makes the crack effect as it travels through the air at high speed, breaking the sound barrier. Yes, as a working whip artist, I can tell you that the "cracker" or "popper" end of a bullwhip can travel over 700 MPH. The leather strand that attaches the cracker to the main body, or THONG, of the whip, is called the Fall. In the old days, the cracker was often made of hemp or horsehair.
This is also associated with the slave masters, who would use the cracker against a slave's skin as punishment or in an attempt to "motivate" the slave. It should be noted that,among those who work with livestock such as cattle, the whip was NOT used to hit the animal, but ONLY to make noise so as to drive the animal in a certain direction. Anybody hitting an animal was usually fired, and sometimes given the lash treatment themselves.
Watch out for the cracker on the end of that whip! You'll put your eye out!"