Source : WordNet®

hypotonicity
     n 1: (of a solution) the extent to which a solution has a lower
          osmotic pressure than some other [ant: {hypertonicity}]
     2: (of muscular tissue) the state of being hypotonic [syn: {hypotonia},
         {hypotonus}] [ant: {hypertonia}, {hypertonia}, {hypertonia}]