a. [ Cf. F. tonigue, Gr. &unr_;. See Tone. ] 1. Of or relating to tones or sounds; specifically (Phon.), applied to, or distingshing, a speech sound made with tone unmixed and undimmed by obstruction, such sounds, namely, the vowels and diphthongs, being so called by Dr. James Rush (1833) “ from their forming the purest and most plastic material of intonation.” [ 1913 Webster ]

2. Of or pertaining to tension; increasing tension; hence, increasing strength; as, tonic power. [ 1913 Webster ]

3. (Med.) Increasing strength, or the tone of the animal system; obviating the effects of debility, and restoring healthy functions. [ 1913 Webster ]

4. (Med.) Characterized by continuous muscular contraction; as, tonic convulsions. [ Webster 1913 Suppl. ]

Tonic spasm. (Med.) See the Note under Spasm. [ 1913 Webster ]

n. [ Cf. F. tonique, NL. tonicum. ] 1. (Phon.) A tonic element or letter; a vowel or a diphthong. [ 1913 Webster ]

2. (Mus.) The key tone, or first tone of any scale. [ 1913 Webster ]

3. (Med.) A medicine that increases the strength, and gives vigor of action to the system. [ 1913 Webster ]

Tonic sol-fa (Mus.), the name of the most popular among letter systems of notation (at least in England), based on key relationship, and hence called “tonic.” Instead of the five lines, clefs, signature, etc., of the usual notation, it employs letters and the syllables do, re, mi, etc., variously modified, with other simple signs of duration, of upper or lower octave, etc. See Sol-fa. [ 1913 Webster ]

a. Tonic. [ R. ] Sir T. Browne. [ 1913 Webster ]

n. (Physiol.) The state of healthy tension or partial contraction of muscle fibers while at rest; tone; tonus. [ 1913 Webster ]