shot

   1. a measure of spirits

   Probably from the way it is discharged into the glass. In the British Isles it is usually measured with an excess of caution, a reprehensible habit that now seems to have spread to America.

   2. a narcotic taken illegally

   Usually by injection:

    The keepers could sell the balance... to other prisoners in need of a shot. (Lavine, 1930)

   3. drunk

   Probably from the slang meaning, finished, although the variant, shot away, does not help that etymology. So long as you are still on your feet, you are unlikely to be more than half-shot:

    ... unlimited wine being dispensed in all the public buildings. The whole population seemed to be half-shot. (Fraser, 1970)

   4. an ejaculation of semen

   When you shoot off:

    It's the only [brothel] where you get three shots for your money. The shot upstairs (fellatio). The shot downstairs (vaginal copulation). And the shot in the room (whisky). (Longstreet, 1956)