- 1 (also tonic water) [uncountable, countable] a clear drink with bubbles in it and a slightly bitter taste, that is often mixed with a strong alcoholic drink a gin and tonic
- 2[countable] a medicine that makes you feel stronger and healthier, taken especially when you feel tired herbal tonics
- 3[countable, uncountable] a liquid that you put on your hair or skin in order to make it healthier skin tonic
- 4[countable, usually singular] (old-fashioned) anything that makes people feel healthier or happier The weekend break was just the tonic I needed.
- 5[countable] (music) the first note of a scale of eight notes
- 6(also tonic syllable) [countable] (phonetics) the syllable in a tone unit on which a change in pitch takes place