tonikos

Greek tonikós meant 'of or for stretching,' from tónos, meaning tension, tone, or a stretched string. In Greek medicine, a tonic was something that restored tension to the body — a remedy that tightened what illness had loosened. Hippocrates used the concept: healthy flesh had good tone; sick flesh was slack. Medicine that restored firmness was tonic.

The word entered English medical vocabulary in the 1600s. Tonic medicines were stimulants and strengtheners — quinine for malaria, iron for anemia, strychnine in small doses for fatigue. The Victorian era was the golden age of tonics. Patent medicine companies sold 'tonic wines' and 'health tonics' that were often little more than alcohol, sugar, and a stimulant. Coca-Cola started in 1886 as Pemberton's French Wine Coca — a tonic.

Tonic water has its own history. British colonists in India mixed quinine — the antimalarial — with sugar and carbonated water to make the bitter medicine drinkable. The gin and tonic was born from medical necessity: the gin made the tonic bearable, and the tonic kept malaria at bay. Winston Churchill reportedly said the gin and tonic had saved more English lives than all the doctors in the Empire.

In music, the tonic is the home note of a key — the note that provides resolution, the pitch everything else relates to. The metaphor is the same: tension and release, stretching and returning. The Greek string stretched to its proper pitch. The body restored to its proper firmness. The melody resolved to its proper note.