high ball: a signal to a train engineer to go ahead
Also spelled highball or high-ball, this signal was originally semaphored by the raising of a ball at the side of the tracks. Later, the conductor or brakeman would wave a lantern in a high arc to signal "full speed ahead." The term was also used figuratively to mean a clear road ahead, as in "We had a highball trail into town." Used as a verb, it meant to move very quickly, not necessarily on a train. A 1961 American Speech article quotes, "Imagine yourself on the seat of an enormous freighter, high-balling it down a West Coast highway."
Around the end of the nineteenth century, highball began to be used as a name for a drink consisting of alcohol and a mixer, such as whiskey and soda. Whether the two meanings are connected is unclear. Were highballs the signal for a party to move full speed ahead? Sophisticates continued to drink highballs until the early sixties, when it became more common to order drinks by their components—"scotch and water" or "gin and tonic," for instance.