What is the meaning of Highball?

A cocktail made from a spirit plus soda water etc.

An all clear or full speed ahead signal.

A very high bouldering problem, often with a hard landing.

Clipping of highball glass, a tall glass tumbler used for serving highballs.

To make an estimate which tends toward exaggeration.

To move quickly; to hightail.

Source: wiktionary.org