a medicine that invigorates or strengthens: a tonic of sulphur and molasses.
anything invigorating physically, mentally, or morally: His cheerful greeting was a real tonic.
Music. the first degree of the scale; the keynote.
Chiefly Eastern New England. soda pop.
Phonetics. a tonic syllable or accent.
pertaining to, maintaining, increasing, or restoring the tone or health of the body or an organ, as a medicine.
invigorating physically, mentally, or morally.
Physiology, Pathology.
pertaining to tension, as of the muscles.
marked by continued muscular tension: a tonic spasm.
using differences in tone or pitch to distinguish between words that are otherwise phonemically identical: a tonic language.
pertaining to tone or accent in speech.
Phonetics. (of a syllable) bearing the principal stress or accent, usually accompanied by a change in pitch.
of or pertaining to a tone or tones.
pertaining to or founded on the keynote, or first tone, of a musical scale: a tonic chord.

1640–50; < Greek tonikós pertaining to stretching or tones. See tone, -ic

tonically, adverb
antitonic, adjective, noun
nontonic, adjective
pretonic, noun, adjective

2. stimulant, restorative, bracer, pickup.

5. See soda pop. Unabridged


a combining form occurring in adjectives that correspond to nouns ending in -tonia: catatonic.

see tonic Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
tonic (ˈtɒnɪk)
1.  a medicinal preparation intended to improve and strengthen the functioning of the body or increase the feeling of wellbeing
2.  anything that enlivens or strengthens: his speech was a tonic to the audience
3.  Also called: tonic water a mineral water, usually carbonated and containing quinine and often mixed with gin or other alcoholic drinks
4.  music
 a.  the first degree of a major or minor scale and the tonal centre of a piece composed in a particular key
 b.  a key or chord based on this
5.  a stressed syllable in a word
6.  serving to enliven and invigorate: a tonic wine
7.  of or relating to a tone or tones
8.  music of or relating to the first degree of a major or minor scale
9.  of or denoting the general effect of colour and light and shade in a picture
10.  physiol of, relating to, characterized by, or affecting normal muscular or bodily tone: a tonic spasm
11.  of or relating to stress or the main stress in a word
12.  denoting a tone language
[C17: from New Latin tonicus, from Greek tonikos concerning tone, from tonostone]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1649, "relating to or characterized by muscular tension," from Gk. tonikos "of stretching," from tonos "a stretching" (see tenet). The meaning "maintaining the healthy firmness of tissues" is recorded from 1684, first extended 1756 to "having the property of restoring to
health." The noun meaning "a tonic medicine" is attested from 1799. The musical sense is first attested 1760, from tone (q.v.).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

tonic ton·ic (tŏn'ĭk)

  1. Of or producing tone or tonicity in muscles or tissue.

  2. Characterized by continuous tension or contraction of muscles, as a convulsion or spasm.

  3. Producing or stimulating physical, mental, or emotional vigor.

An agent, such as a medication, that restores or increases body tone.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Britannica


in music, the first note (degree) of any diatonic (e.g., major or minor) scale. It is the most important degree of the scale, serving as the focus for both melody and harmony. The term tonic may also refer to the tonic triad, the chord built in thirds from the tonic note (as C-E-G in C major). See also tonality.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
As befits the pointy-headed elevation of all simple things, gourmet attention
  is now being paid to the humble gin and tonic.
After the solitude of graduate research, that's a powerful tonic.
The best way is a gin and tonic in the lounge and a couple on the flight.
Hair tonic poisoning occurs when someone swallows this substance.
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