Real Dictionary

bourbon
variable noun: Bourbon is a type of whisky that is made mainly in America.

Bourbon in American English
a whiskey distilled from a fermented mash of not less than 51 percent corn grain and stored in charred new oak containers for not less than two years
designating, of, or made with such whiskey
name of the ruling family of France (1589-1793; 1814-48, from 1830 to 1848 as the Orléans1 branch); of Spain (1700-1808; 1813-1931; 1975- ); of Naples and Sicily (1734-1806; 1815-60), united as the kingdom of the Two Sicilies, 1815; and of various duchies
noun: a member of a French royal family that ruled in France 1589–1792, Spain 1700–1931, and Naples 1735–1806, 1815–60

bourbon in British English
noun: a member of the European royal line that ruled in France from 1589 to 1793 (when Louis XVI was executed by the revolutionaries) and was restored in 1815, continuing to rule in its Orleans branch from 1830 until 1848. Bourbon dynasties also ruled in Spain
noun: a whiskey distilled, chiefly in the US, from maize, esp one containing at least 51 per cent maize (the rest being malt and rye) and aged in charred white-oak barrels