adj

• (physics, pathology) Pertaining to tension, especially of muscles.
  "Out in front and across the street, Doc noted half a dozen or so young men, not loitering or doing substances but poised and tonic, as if waiting for some standing order to take effect."
• (medicine, neuroscience) In a state of continuous unremitting action.
  "Peter Redgrave (2007) Basal ganglia. Scholarpedia, 2(6):1825. GABAergic neurones in the basal ganglia output nuclei have high tonic firing rates (40-80 Hz)."

noun

• (US, Eastern Massachusetts, dated) Any of various carbonated, non-alcoholic beverages; soda pop.
• (figuratively) Someone or something that revitalises or reinvigorates.
  "Charlie ain't no Nazi / She likes to wear her leather boots / 'Cause it's exciting for the veterans / And it's a tonic for the troops."

verb

• (medicine, archaic) To restore or invigorate.
  "When all signs of effusion, dulness, pain, œgophony, and cough had disappeared he was dieted, stimulated, and tonicked."

adj

• (music) Pertaining to or based upon the first note of a diatonic scale.