- tonic (n.1)
- "a tonic medicine," 1799, from tonic (adj.).
- tonic (adj.)
- 1640s, "relating to or characterized by muscular tension," from Greek tonikos "of stretching," from tonos "a stretching" (see tenet). The meaning "maintaining the healthy firmness of tissues" is recorded from 1680s, first extended 1756 to "having the property of restoring to health."
- tonic (n.2)
- in the musical sense, 1760, from tone (n.) + -ic. Related: Tonicity.