Antonyms for Isotonic (opposite meaning)
WordNet sense 1 ((of a solution) having a lower osmotic pressure than a comparison solution):
hypotonicWordNet sense 2 ((of a solution) having a higher osmotic pressure than a comparison solution):
hypertonicWordNet sense 3 (of or involving muscular contraction in which tension increases while length remains constant):
isometricFrom the ODE community, based on WordNetadd/edit