tonic

Short definition from Wiktionary

Adjective

1. 1
   Pertaining to tension, especially of muscles.
2. 2
   Restorative, curative or invigorating.
3. 3
   In a state of continuous unremitting action.
4. 4
   Pertaining to or based upon the first note of a diatonic scale.
5. 5
   Pertaining to the accent or stress in a word or in speech.
6. 6
   Of or relating to tones or sounds; specifically (phonetics, dated) being or relating to a speech sound made with tone unmixed and undimmed by obstruction, i.e. a vowel or diphthong.

Noun

1. 1
   A substance with medicinal properties intended to restore or invigorate.
2. 2
   Tonic water.
3. 3
   Any of various carbonated, non-alcoholic beverages; soda pop.
4. 4
   Someone or something that revitalises or reinvigorates.
5. 5
   The first note of a diatonic scale; the keynote.
6. 6
   The triad built on the tonic note.
7. 7
   A tonic element or letter; a vowel or a diphthong.

Verb

1. 1
   To restore or invigorate.