tonic \ton"ic\, a. cf. f. tonigue, gr. ?. 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
see also:
tone tonic spasm spasm