tonicity

/toʊˈnɪsəti/
noun
  1. The state of having normal muscle tone or firmness.
    • The physical therapist checked the tonicity of the patient's legs after the injury.
    • Adequate hydration is important for healthy skin tonicity.
    • Regular exercise helps maintain good tonicity in your muscles.
  2. The osmotic pressure or concentration of a solution, especially in biology.
    • The tonicity of the saline solution must match that of human blood for safe IV use.
    • In biology class, we learned how tonicity affects cell size in different liquids.
    • The tonicity of the surrounding fluid determines whether a plant cell will swell or shrink.