Definition of: isotonic

(ī′sə·ton′ik) adjective
1. Having the same tonicity.
2. Physiol. a Having the same osmotic pressure on opposite sides of a membrane: said of solutions, especially blood or plasma: distinguished from hypertonic: also isosmotic. b Denoting a muscle which contracts against a small but uniform tension or the curve of such a contraction.
3. Music Pertaining to, characterized by, or having equal tones. [<Gk. isotonos having equal accent or tone <iso- equal + tonos accent, tone]
—i·so·to·nic·i·ty (ī′sə·tō·nis′·ə·tē) noun