A white ball hauled up to the crossbar indicated that the track was clear; a black ball, run up half way, meant stop. This was the origin of the use of the word "highball" to indicate a clear line ahead, which is still used in U.S.A. railway practice.1946 November and December, “Notes and News: The American Highball”, in Railway Magazine, page 382:
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Climbing, Hobbies, Lifestyle, Sports A very high bouldering problem, often with a hard landing.
2014, EpicTV.com Austrian all rounder Alex Luger climbs what he describes as a highball boulder problem and what most people would call a solo.
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Abbreviation, Clipping Clipping of highball glass, a tall glass tumbler used for serving highballs.
It's great for serving heavier drinks in. Highballs and pint glasses are excellent substitutes.2021, Kate Calder, Three Ingredient Cocktails: 60 Drinks Made in Minutes:
Booster-equipped 628 highballs west at Glen Lake, Minn., back in 1947.1959, Steam's Finest Hour, edited by David P. Morgan, Kalmbach Publishing Co. (photo caption)
The water-level route, the whistle and the loud staccato exhaust of this great engine recalled most vividly memories of the New York Central Hudsons highballing along the Hudson River between Harmon and Albany!1960 October, P. Ransome-Wallis, “Modern motive power of the German Federal Railway: Part Two”, in Trains Illustrated, page 613: