1. Having uniform tension, as the fibers of a contracted muscle.
2. Of a solution, having the same osmotic pressure as the fluid phase of a cell or tissue.

1. A muscle exercise in which the muscles remain under relatively constant tension; such as, when lifting weights or when doing other exercises.
2. A biological term denoting a solution in which body cells can be bathed without a net flow of water across the semipermeable cell membrane. It also refers to a solution having the same tonicity as some other solution with which it is compared; such as, physiological salt solution and the blood serum.