Whiskey, rum, gin, brandy, etc., as distinct from wine and beer; spirits; strong waters (1879+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with hard liquor
Distilled alcoholic beverages, such as gin or whiskey. For example, We're serving wine and beer but no hard liquor. The hard here refers to their high alcoholic content, which is also true for
hard cider, although the latter is not distilled but has simply fermented.