A tonic is something that makes you feel stronger, healthier, or more energetic. When your grandmother suggests a walk in the fresh air as a tonic for your gloomy mood, she means it will revive your spirits and make you feel better. In old-fashioned medicine, tonics were drinks or mixtures (sometimes with questionable ingredients) that claimed to restore health and vigor.

Today we mostly use tonic figuratively: a funny book might be a tonic for a boring afternoon, or good news could be a tonic for someone who's been worried.

Tonic also has a specific meaning in music: it's the home note of a scale, the note that feels most stable and complete. In the key of C major, C is the tonic. When a song ends on the tonic note, it feels finished and satisfying, like coming home after a long journey.

You might also hear about tonic water, a fizzy drink with a slightly bitter taste from quinine. It's called tonic because quinine was originally used as medicine. People often mix it with other drinks, but you can drink it plain if you enjoy its distinctive flavor.