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 ]