tonic
Pronunciation: /ˈtɒnɪk/
noun
- 1a medicinal substance taken to give a feeling of vigour or well-being.
- something with an invigorating effect: being needed is a tonic for someone at my age
- 2short for tonic water.
adjective

Origin:
mid 17th century: from French tonique, from Greek tonikos 'of or for stretching', from tonos (see tone)