Isotonic

a.
  1. Having or indicating, equal tones, or tension.
  2. (Physiology, Biochemistry) Having an osmotic pressure (tonicity) equal to that of a reference solution; -- of aqueous solutions. Contrasting with hypotonic and hypertonic. See hypertonic.
    3. Isotonic system (Mus.),
    a system consisting of intervals, in which each concord is alike tempered, and in which there are twelve equal semitones.