tonic

Relating to the first note of a musical scale; the keynote.

"The piece resolves to the tonic chord."

Something that makes you feel healthier, more vigorous, or refreshed.

"A walk in the fresh air was a real tonic."

Relating to or producing normal tone or tension in muscles or organs.

"The doctor noted a tonic spasm."

A carbonated drink, often with quinine, typically mixed with gin.

"He ordered a gin and tonic at the pub."