What is the term for the instrument used to extract a sample of whiskey from a barrel?

The term that accurately describes the instrument used to extract a sample of whiskey from a barrel is "whisky thief." This tool is specifically designed to draw whiskey from a barrel without wasting the contents. It typically has a long, slender shape that allows it to reach into the barrel and a mechanism that facilitates the collection of the liquid sample.

The other terms provided, while they might seem intuitive, do not reflect the specific industry terminology. "Sample thief" may suggest a similar function but is less commonly recognized in the context of whiskey sampling. "Barrel extractor" implies a different mechanism or tool that might not be specific to the act of sampling whiskey. "Whiskey tester," on the other hand, suggests a device used for testing or analyzing whiskey, which is distinct from sampling it directly from a barrel. Therefore, "whisky thief" stands out as the correct and widely accepted term within the spirits industry.