tonic

adj

1. Pertaining to tension, especially of the muscles.

   “Out in front and across the street, Doc noted half a dozen or so young men, not loitering or doing substances but poised and tonic, as if waiting for some standing order to take effect.”

2. Restorative; curative; or invigorating.

   “The arrival of the new members had a tonic effect on the team.”

3. In a state of continuous unremitting action.

   “Peter Redgrave (2007) Basal ganglia. Scholarpedia, 2(6):1825. GABAergic neurones in the basal ganglia output nuclei have high tonic firing rates (40-80 Hz).”

4. (not-comparable)Pertaining to or based upon the first note of a diatonic scale.
5. (not-comparable)Pertaining to the accent or stress in a word or in speech.
6. (not-comparable)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. (uncountable, usually)A substance with medicinal properties intended to restore or invigorate.

   “We used to brew a tonic from a particular kind of root.”

2. (uncountable, usually)Tonic water.
3. (US, dated, uncountable, usually)Any of various carbonated, non-alcoholic beverages; soda pop.
4. (figuratively, uncountable, usually)Someone or something that revitalises or reinvigorates.

   “Charlie ain't no Nazi / She likes to wear her leather boots / 'Cause it's exciting for the veterans / And it's a tonic for the troops.”

   “'You're a tonic, Dee,' she said. 'And a real friend. Thanks.'”

   “The result is the perfect tonic for Newcastle, coming at the end of a week that saw the departure of Andy Carroll to Liverpool on Monday and an injury to Shola Ameobi during Wednesday's defeat at Fulham.”

5. The first note of a diatonic scale; the keynote.
6. The triad built on the tonic note.
7. A tonic element or letter; a vowel or a diphthong.

verb

1. (archaic)To restore or invigorate.

   “When all signs of effusion, dulness, pain, œgophony, and cough had disappeared he was dieted, stimulated, and tonicked.”

   “The Persians, as a nation, were first to discover that fish were edible. The time is fixed at about 3000 B.C. This was their secret for some centuries—until the Assyrians learned about the elegance of fish for tonicking the brain.”