/ ˈtɒnɪk; NAmE ˈtɑːn-/ noun
1.
(also ˈtonic water ) [ U , C ] a clear fizzy drink (= with bubbles in it) with a slightly bitter taste, that is often mixed with a strong alcoholic drink, especially gin or vodka :
a gin and tonic
2.
[ C ] a medicine that makes you feel stronger and healthier, taken especially when you feel tired :
herbal tonics
3.
[ C , U ] a liquid that you put on your hair or skin in order to make it healthier :
skin tonic
4.
[ C , usually sing. ] ( old-fashioned ) anything that makes people feel healthier or happier :
The weekend break was just the tonic I needed.
5.
[ C ] ( music ) the first note of a scale of eight notes
6.
(also ˌtonic ˈsyllable ) [ C ] ( phonetics ) the syllable in a tone unit on which a change in pitch takes place
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WORD ORIGIN
mid 17th cent.: from French tonique , from Greek tonikos of or for stretching, from tonos tension, tone, from teinein to stretch.