Noun

1. A carbonated beverage containing quinine, which is a medicine. It is used to make gin and tonic, a primarily recreational drink.

   Blue, Anthony Dias, Mixology: Gin & Tonic in Drinks, the Magazine of Fine Wine, Spirits, and Living, Spring 2009, p8:

   • Tonic water's active ingredient is quinine, a chemical compound derived from the bark of the cinchona tree, native to South America. This alkaloid has long been known to relieve the pain and fever of malaria and other tropical diseases, making it a staple "tonic" in warm-weather countries.