1. Having equal tension.
4. Pertaining to a solution that has the same tonicity as some other solution with which it is compared. For example, blood serum is isotonic to a physiologic salt solution. Solutions that have same tonicity will result in no net flow of water across the cell membrane.
Word origin: ISO– + Greek tonos, tension; see tone + –IC.
Related forms: isotonically (adverb), isotonicity (noun).
Related phrases: isotonic exercise, isotonic contraction, isotonic solution.