Tonic
mid 17th century: from French tonique, from Greek tonikos ‘of or for stretching’, from tonos (see tone).
wiktionary
From Ancient Greek τονικός(tonikós), from τόνος(tónos). 17th century writers believed health to be derived from firmly stretched muscles, thus tonic; the extension of tonic medicine appeared in the late 18th century. Surface analysis as classical compound: tone + -ic.
From tone + -ic.
etymonline
tonic (adj.)
1640s, "relating to or characterized by muscular tension," from Greek tonikos "of stretching," from tonos "a stretching," from PIE root *ten- "to stretch." The meaning "maintaining the healthy firmness of tissues" is recorded from 1680s, first extended 1756 to "having the property of restoring to health." Related: Tonical (1580s).
tonic (n.1)
"a tonic medicine," 1799, from tonic (adj.). From 1873 (in gin and tonic) as short for tonic water (1861 as a commercial product, water infused with quinine), so called because held to aid digestion and stimulate appetite.
tonic (n.2)
in the musical sense, 1760, short for tonic note, from tone (n.) in the musical sense + -ic. Related: Tonicity.
