Definition of: tonic

(ton′ik) adjective
1. Having power to invigorate or build up; bracing.
2. Pertaining to tone or tones; specifically, in music, pertaining to the keynote.
3. In art, denoting the general color effect and the light and shade in a picture or scene.
4. Physiol. a Of or pertaining to tension, especially muscular tension. b Rigid; unrelaxing: tonic spasm.
5. Ling. a Of or pertaining to musical intonations or modulations of words, sentences, etc. b Designating languages which distinguish words of identical or very similar form by variations in tone or pitch, as Chinese.
6. Phonet. a Stressed, as a syllable. b Obs. Voiced.
—noun
1. Med. A drug that gradually restores the normal tone of organs from a condition of debility.
2. Whatever imparts vigor or tone.
3. The basic note of a key; keynote. [<Gk. tonikos <tonos sound, tone]